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Full text of "Principles and practice of agricultural analysis [microform] : a manual for the study of soils, fertilizers, and agricultural products : for the use of analysists, teachers, and students of agricultural chemistry"

Principles and Practice 



OF 



Agricultural Analysis 



A Manual for the Study of Soils, Fertilizers, and 

Agricultural Products 



For the Use of Analysts, Teachers, and Students of Agricultural 

Chemistry 



SECOND EDITION. REVISED AND ENLARGED 



VOLUME II 



FERTILIZERS AND INSECTICIDES 



BY HARVEY W. WILEY, A.M., Ph.D. 



EASTCN. PA. 

THE CHEMICAL PUBLISHING CO. 

1908 



PREFACE TO VOLUME SECOND 



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Copyright, 1908, by Harvey W. Wiley. 



In this volume an attempt has been made to treat the subject of 
fertilizers and fertilizing materials in the manner followed in 
the first volume with soils. The general principles of fertilizer 
manufacture and application have been presented in so far as 
they seemed to throw light on the rational method of examination 
and analysis. The standard methods of analysis in use in this 
and other countries, have been presented with sufficient 'fullness 
for the guidance of the skilled worker, and the information of 
the student. To those who make use of a book only for routine 
work or for preparation for an examination, this volume, as its 
predecessor, will be found to have little attraction. This fact, 
however, will not be a cause of regret to the author whose pur- 
pose has been, avowedly, to present to the busy worker and stu- 
dent a broad view of a great subject which each one does not have 
the time to search out for himself. 

It is a matter of regret, however, that the contents of the vol- 
ume have again exceeded all expectations. It was found im- 
practical)le to secure any greater condensation without depart- 
ing from the purpose, and impairing the completeness of the 
work. When work is done with no prospect of financial com- 
pensation, it is gratifying to find it appreciated,- and the author 
will be content to have this volume meet with as kindly a recep- 
tion as has been accorded volume one. 

HARVitY W. Wiley. 

Washington, D. C, 
End of July, 1893. 



333S5 



CONTENTS 



PART FIRST 



PREFACE TO SECOND EDITION 



A great part of the material relating to the occurrence and 
analysis of ammonia, nitrous and nitric acid printed in the first 
volume of the first edition of this work has been rewritten and 
transferred to this volume. This rearrangement has resulted 
in making the first and second revised volumes of approximately 

the same size. 

All the matter of this volume has been rewritten and brought 
down to date. New features of moment are those relating to the 
production of nitric acid for manurial purposes from cyanamid 
and by direct electric oxidation of the nitrogen of the air. A 
chapter on the analysis of insecticides has also been added. 

While not intended in any way as a laboratory guide it is 
hoped this volume may be even more highly appreciated than 
in its first form by the student, the investigator and the teacher. 

H. W. Wiley. 

November y i(^o8» ■ .-•• ■ •• •••;_ 



,... ^..\-- ' •'.■f . .... 



\" 



Definitions, Sampling and Preliminary Treatment, pp. 1-22. — Waste 
matters as fertilizing materials ; Waste materials as fertilizers ; Valuation 
of fertilizers; Trade valuations of fertilizers; General principles of sampl- 
ing; Object of sampling; Sampling a gas; Sampling a liquid; Sampling a 
solid; Subdivision of sample; Sampling of fertilizers; Mixed fertilizers; 
Barn-yard manures; Sampling of materials used for road building; 
Methods of sampling; Preparation of sample in laboratory. 

Drying Samples of Fertilisers, pp. 22-25. — Difficulties of desiccation; 
Official methods; General observations; Moisture in monocalcium phos- 
phates. 

Mineral Phosphates, pp. 25-40. — Natural occurrence of phosphates; 
Florida phosphates; Tennessee phosphates; Occurrence of black phos- 
phate ; Occurrence of v^hite phosphate ; Origin of the white phosphates ; 
Utilization of white phosphate. 

Statistics and Composition, pp. 40-49. — Tennessee phosphates ; Blue phos- 
phate; South Carolina phosphates; Magnitude of product; Production in 
the United States; Marketed production; World's production; Quantity 
of phosphoric acid removed by crops ; General conclusions. 

Analytical Processes, pp. 49-121. — Constituents to be determined; Dis- 
solving phosphates ; Incineration ; Loss of phosphoric acid on incineration ; 
Official methods; General methods for estimating phosphoric acid; Prepa- 
ration of reagents ; Formula for the reactions ; Official method for total 
phosphoric acid; Influence of insoluble silica; Use of tartaric acid; Water- 
soluble phosphoric acid ; Citrate-insoluble phosphoric acid ; Examination of 
the pyrophosphate ; Determination of available phosphoric acid ; Interna- 
tional methods ; Molybdic acid method ; French official method ; Swedish 
official method; Dutch official method; Sources of error in the molybdate 
method ; Influence of aluminum, magnesium and calcium ; Color of the 
magnesium pyrophosphate; The citrate method; German experiment 
station method ; The Swedish citrate method ; Methods adopted by the 
Brussels Congress; Dutch citrate method; Method of Lasne ; Compara- 
tive accuracy of the citrate and molybdate methods; The citrate precipi- 
tate purity; The citrate method applied to samples with small content 
of phosphoric acid; Direct precipitation of the citrate-soluble phosphoric 
acid.;. Detet^mination of phosphoric acid with preliminary precipitation as 



VI 



CONTENTS 



stannic phosphate; Phosphoric acid soluble in ammonium citrate; Arbi- 
trary determination of reverted phosphoric acid; Theory of revision; 
Influence of movement; Digestion api^aratus for reverted phosphates. 
Comparison of results ; Huston's mechanical stirrer ; Precipitation of 
the water and citrate-soluble phosphoric acid; Veitch's method for 
available phosphoric acid; Availability of phofiphatic fertilizers. 

Direct Weighing of the Phosphomolybdate Precipitate, pp. 122-130.— 
Method of Hanamann; Method of Lorenz ; Method of Woy; Berju's 
modification; Method of Graftiau; Method of Pellet; Cladding's modifica- 
tion. 

Volumetric Determination of Phosphoric Acid, pp. i30-i78.~Classifica- 
tion of methods; Uranium method; Precipitation of phosphates in pres- 
ence of citrate; Magnesium citrate solution; Filtration and washing; 
Standard solution of uranium nitrate; typical solution of phosphoric 
acid- Titration of uranium solution; Determination of phosphoric acid 
in superphosphates ; Determination of soluble and reverted phosphoric acid ; 
Conclusions; Pemberton's volumetric method; Alkalimctric estimation of 
phosphoric acid; Comparison of weighing and titrating methods; Esti- 
mation of phosphoric acid as a lead compound ; Water-soluble phosphoric 
acid; Estimation of phosphoric acid in the presence of iron ; Methods of the 
international steel standards committee; Calculating results; The silver 
method. 

Technical Determination of Phosphoric Acid, pp. 179-189— Desirability 
of methods ; Reagents ; Manipulation ; Citrate method ; Uranium method ; 
Determination of phosphoric acid in basic slags ; Determination of phos- 
phoric acid in superphosphates ; Determination of free acid in phosphates ; 
Ostersetzer's method. 

Basic Phosphatic Slags, pp. 190-223.— Uses of basic slag; Hiitory and 
manufacture; Quantity made; Process of manufacture; Composition 
of slag phosphate; Molecular structure; Solubility; Solvents; Method 
of estimation; Method used at the Halle agricultural station; Dutch 
method ; Estimation of citrate-soluble phosphoric acid ; Wagner's method ; 
Method of the German agricultural experiment stations; Preparation 
of the citric acid extract; Direct precipitation method; German method 
for slags rich in silicic acid ; Bottcher method ; Separation of silicic acid ; 
Estimation of total phosphoric acid; American methods; German manu- 
facturer's method; Estimation of lime; Detection of adulteration. 

Determination of Other Constituents in Natural Phosphates, pp. 224- 
260.— Water and organic matter ; Carbon dioxid ; Soluble and insoluble 
maticr; Silica and insoluble bodies; Loss of silica and fluorin ; Esti- 
mation' of lime; Ammonium oxalate method; Method of Tmmendorff; 
Estimation of iron and alumina; The acetate method; Method of Hess; 
Method of E. Glaser; Jones' variation; Crispo's method; Variation of 



CONTENTS 



Vll 



the alcohol method ; Variation of Marioni and Tasselli ; Method of Krug 
and McElroy; Method of Wyatt; Separation of iron and aluminum 
phosphates ; Methods of the German fertilizer association ; French meth- 
od; Method of Lasne ; Comparison of methods for iron and alumina; 
Sources of error; Effect of iron salts; Eflfect of calcium salts; Effect of 
sulfates ; Effect of fluorin ; Separation of alumina with phenylhydrazine ; 
General conclusions. 

Occurrence of Fluorin in Phosphates, pp. 261-276. — Significance of 
fluorin; Method of Berzelius ; Chatard's modification; Wyatt's modifica- 
tion; Method of Rose; Burk's modification of Carnot's method; Method 
of Lasne; Carnot's modification; Protection of glassware from fluorin; 
Fluorin in bones ; lodin in phosphates ; Chromium in phosphates ; Vanad- 
iurji in phosphates. 

Superphosphate Manufacture, pp. 277-286. — Chemical changes in manu- 
facture ; Reaction with fluorids ; Reaction with carbonates ; Solution of 
the iron and alumina compounds; Quantity of sulfuric acid; Use of 
phosphoric acid ; Fixation of phosphoric acid ; Absorption of phosphoric 
acid ; Availability. 

PART SECOND 

Nitrogen in Fertilizers, Drainage Waters, Etc., pp. 287-300. — Kinds of 
nitrogen in fertilizers; States of nitrogen; Nitrogen in seeds and seed 
residues ; Nitrogen in seaweed ; Dried blood and tankage ; Horn, hoof, 
and hair ; Nitrogen in fish ; Nitrogen from birds ; Waste nitrogen ; 'Nitro- 
gen in soils; Deposits of nitrates; Quantity of nitrates used; Nitrate 
deposits in Chile; Nitrate deposits in California; Functions of sodium 
nitrate; Composition of nitrate deposits; Commercial forms of nitrates; 
Composition of Chile saltpeter; Application of saltpeter to the soil. 

Utilization of the Nitrogen of the Air as a Fertilizing Material, pp. 
301-320. — Activity of leguminous plants; Activity of other than legumin- 
ous plants ; Accumulation of atmospheric nitrogen in the soil ; Manufac- 
ture and use of cyanamid ; Cyanamid compound as a fertilizer ; Utiliza- 
tion of atmospheric nitrogen; Development of the fixation of atmos- 
pheric nitrogen; Properties of calcium cyanamid; Production of nitric 
acid by electric action ; Method of Birkeland and Eyde ; Manufacture 
of nitrate of lime ; Quantity of nitric acid by electric action ; Absorption 
and concentration of product ; Method of Moscicki ; Production of 
nitric acid in the United States by electric action. 

Methods of Determining Nitrogen. Volumetric Method, pp. 3,21-2,2,7. — 
Classification of methods; Determination of state of combination; 
Microscopic examination ; Ofiicial method ; Copper oxid method ; Note 
on copper oxid method; Description of apparatus; Variation of Bureau 
of Chemistry method of Johnson and Jenkins ; Calculating results ; 



Vlll 



CONTENTS 



Reading the barometer; Tension of aqueous vapor; Tables for calculat- 

ing results. 

Methods of Determining Nitrogen-Continued. Soda-Ume Process, pp. 
338-34S.-The official method; The Fretich method; 1 he hydrogen meth- 
od ; Coloration of the product ; General considerations ; The Ruffle method ; 
Observations; Beyer's modification. 

Method of Determining NUrogen.-Continued. The Moist Combustion 
Process pp. 346-372.- Method of Kjeldahl; Theory of the reaction; 1 repar- 
ation of reagents ; Modification of the process ; Method of Wilfarth ; Dutch 
method; German method; The Official method not applicable in the 
presence of nitrates; Apparatus employed; The Gunning modification; 
Reactions of the Gunning process. 

Method of Determining Nitrogen.-Continued. Changes in Kjcldahl 
Method to Include Nitric ^cid, pp. 373-382.-Modifications of Asboth ; Var- 
iation of Jodlbauer; The Dutch method; The Halle method; The salicylic 
acid method; Use of zinc sulfid and sodium thiosulfate; Theory o the pro- 
cess; The official method; Gunning method for mtric acid; The official 
Gunning method. 

Determination of Nitrogen in Definite Forms of Combination, pp. 
382-390.-Introductory considerations; Nitrogen as ammonia; Method 
of Boussingault ; Nitrogen as thiocyanates ; Separation of proteid from 
amid nitrogen; Separation of nitric and ammoniacal nitrogen; French 
method; German method; Perchloric acid in Ch-le saUpeter. 

The Nitric Acid Process, pp. 39i-424.-Occurrence of oxidized nitro- 
gen- Method of Schloesing; Schloesing's modified method ; French agri- 
cultural method; Method of French sugar chemists; Method of Schloes- 
ing and Wagner; Modification of Warington; Preparation of the samples; 
Measurement of the gas; Spiegel's modification; de Koninck s modifi- 
cation; Schmidt's process; Merits of the ferrous chlorid process; The 
Crum-Frankland process; Warington's modification; Woy's method; 
Lunge's nitrometer; Utility of the method; Method of Gantter; Analysis 
of Chile saltpeter; Method of difference. 

Estimation of Nitric Acid by Oxidation of a Colored Solution. Indigo 
Meawd. pp. 425-43^. -Method of Marx; Method of Boussingault ; 
Method of Warington; Experimental data; General directions. 

Determination of Nitric Acid by Reduction to Ammonia, pp. 433-440.- 
Classification of methods; Reduction in alkaline solutions; Qualitative 
tests for nitrates; Sodium-amalgam methods; Method of the Mockern 
agricultural station ; The Halle zinc-iron method ; Method of Beck ; 
Method of Devarda ; Variation of Stoklasa ; Method of Sievert. 

Reduction in an Acid Solution, pp. 44i-446.-The sodium-amalgam pro- 
cess; Method of Schmitt;- Method of Ulsch; Ulsch method applied to 
mixed fertilizers ; Kriiger's method. 



CONTENTS 



IX 



Reduction by Electric Current, pp. 447-449.— Method of Williams- 
Warington ; Nitrogen in rain water ; Determination of ammonia ; Prep- 
aration of the copijer-zinc couple; Aluminum-mercury couple. 

lodomctric Estimation of Nitric Acid, pp. 450-454-— Method of de Kon- 
inck and Nihoul; McGowan's apparatus; Method of Gooch and Gruener. 

Estimation of Nitric Acid by Colorimetric Comparison, pp. 455-467. — 
Delicacy of the method; Hooker's method; Influence of other bodies; 
Phenylsulfuric acid method; Method of Gill; Variation of Johnson; 
Estimation of nitric in presence of nitrous acid; Piccini process; Colors 
produced by diphenylamin. 

Estimation of Nitrous Acid, pp. 467-476.— Metaphenylenediamin meth- 
od; Sulfanilic acid method; Preparation of sulfanilic acid; Method of 
Mason; Lunge and Lwoff method; Use of starch as indicator; Method 
of Chabrier; Ferrous salt process. 

Volumetric Process for Nitrous Acid, pp. 477-479- — Decomposition 
with potassium ferrocyanid ; General observations. 

Determination of Free and Albuminoid Ammonia, pp. 480-484. — Ness- 
ler process; Nessler reagent; Conduct of the analysis; Ilosvay's modi- 
fication ; Pure water. 

PART THIRD 

Potash and Fertilising Materials in Fertilisers, pp. 485-526. — Intro- 
duction; Occurrence of Potash; Historical sketch; Deposits at Stassfurt; 
Deposits in Alsace; Mining the salts; Concentrating the salts; Compo- 
sition of crude salts; Kainit; Carnallit ; Polyhalit ; Kruget ; Sylvin ; 
Sylvinit; Kieserit ; Schonit; Potassium sulfate; Potassium magnesium 
carbonate; Potash in factory residues; Production of crude salts; 
Production of concentrated potash salts ; Consumption of potash ; 
Amount of potash used in the different states; Changes in potash salts; 
Theory of deposition; Geological relations; van't Hoff's theory; Dia- 
grams of crystallization; Potash from feldspar; Cushman's investiga- 
tions; Experiments with potash feldspar; Effects of ground feldspar; 
Extraction of potash from ground rocks ; General conclusions. 

Organic Sources of Potash, pp. 526-537. — Tobacco stems and waste; 
Cottonseed hulls and meal ; Wood ashes ; Fertilizing value of wood ashes ; 
Avaibbility of potash in ashes; Potash in beet molasses; Potash in win- 
ery residue; Insoluble potash in plants; Forms of potash in fertilizers; 
Quantity of potash removed by crops. 

Methods of Analysis of Potash. Preparation of Sample, pp. 538-577-— 
Destruction of organic matter by ignition; Destruction of organic mat- 
ter by sulfuric acid ; Qualitative detection ; The platinic-chlorid method ; 
Official method; Optional method; French m<^thod ; German method; 
Dutch method; Swedish method; Methods of the potash syndicate; 



CONTENTS 



Methods for concentrated salts; Methods for ^'f ^f^^ ^i*;/ .t^.^^: 
.rr. r.f ^nliiHons- Lunge's modification of technical methods, i tie oar 

r: a.atre:hod : L^hod of '^^o°<'-v^f-'";fr lu 1= 

Moore's method modified by Veitch ; Apphcafon of he platuu m 
ncthod ..presence of sulfates; Rapid control method; We,ghn,g the 

Shut" a^s metallic platinum; Sources of --r in the platmur^ me h^ 

od- Effect of concentration; Differences m crystallme form, Factors tor 

.ot'ash Recovery of platinum waste; Preparation of chlor-p atm.c ac.d. 

Estimation of Potash as Pcrchloratc, pp. 578-593.-General prmc^les. 
SchSs modification; Kaspar's method for ^^<;^^^}"^J^^_ 
acid- Kreider's method; Keeping properties of perchloric acid, lech 
niue of he process; Disturbing factors; Removal of ^-^-^^ ^' 
3i«tion to crude potash salts; Influence of carbonates; Applicability 
of the process; Accuracy of the process. 



LIST OF ILLUSTRATIONS 



PART FOURTH 



Miscellaneous Fertilisers. PP- 594-625 -Classihcation Forms of 1 me 
Application of lime; Action of lime; Best forms of lime; Analysis of 
Hme Gypsum; Analysis of gypsum; Solubility in sodium carbonate 

Smmo/'salt; 'Green vitriol; Hen ^^^-^^^^^^^^^^''^T^^^^^^ 
Total phosphoric acid in guanos; Waste leather; Analysis of w^od ashes 
Ca bon sand, and silica; Phosphates and alkaline earths; Method of 
ScElroy Early official methods for alkalies; Official methods for the 
Lrminltion of inorganic plant constituents; Sulfur m plants; Chlorm 
fnnZs Seating results of fertilizer analyses; The elemental system 
The' oS;tions ;;'the elemental system; The advantages of the elemental 
system- The ionic system; General conclusions. 

Insecticides and Fungicides. PP- 625-653.-Kinds of ^^^?^^ 
classification of insecticides; Paris green; Methods of ^^^^y^'' ^ ^''"^^l 
on o methods of analysis; Green arsenoid; London purple; Me hod 
of analysis • Discussion of methods of analysis ; Lead arsenate ; Methods 
oi analy si : Insecticides for external sucking insects; Soaps; Caustic soda 
aL Sash Methods of analysis; Lime-sulfur-salt mixture; Methods of 
aniy^s^ K^ emulsion; Tobacco and tobacco extract ; Determi- 

: ofof nicotin; Potassium cyanid; Carbon disulfid ; ^:^^-^^_ 
stored grains; Insecticides for animal parasites; Fungicides, Forn aide 
hyd ; Bordeaux mixture; Copper sulfate; Official methods of ana^ys , 
Discussion of methods of analysis; Statement of Insecticide analyses. 
Scheme for reporting results of analysis. 



J?igure 1. Apparatus for crushing mineral fertilizers i2 

*' 2. Plate grinder for minerals * 3 

" 3. Shaking apparatus for superphosphates 92 

" 4. Shaking machine for ammonium magnesium phosphate 96 

" 5. Rossler ignition furnace • • • 97 

Plate, figure 6. Huston's agitating machine opposite 116 

Figure 7. Huston's mechanical stirrer 1 1^ 

" 8. Jones' reduction tube ^7^ 

" 9. Reductor and filter attachment ^75 

** 10. Permanganate burette ^75 

" II. Wagner's digestion apparatus for slags 202 

" 12. Lasne's apparatus • • 268 

Plate, figure 13. Wild duck's and eggs on Layson Island opposite 291 

Figure 14. Mercury pump and azotometer 32o 

" 15. Moist combustion apparatus of the Halle agricultural laboratory 359 

" 16. Distillation apparatus of the Halle agricultural laboratory 361 

Plate, figure 17. Hood opposite 367 

Plate, figure 18. Distilling apparatus opposite 367 

Figure 19. Trap of distilling apparatus 3^9 

" 20. Schloesing's apparatus for nitric acid 392 

" 21. Schlucsing-Wagner apparatus 398 

" 22. Warington's apparatus for nitric acid 399 

" 23. Schulze-Tiemann's nitric acid apparatus 404 

" 24. Spiegel's apparatus for nitric acid 408 

" 25. DeKonnick's apparatus 409 

26. End of delivery tube 4io 

*' 27. Schmidt's apparatus 412 

" 28. Lunge's nitrometer 4^5 

" 29. Lunge's improved apparatus 4^7 

" 30. Lunge's analytic apparatus 420 

" 31. Gantter's nitrogen apparatus 422 

" 32. Halle nitric acid apparatus 43^ 

33. Stoklasa's nitric acid apparatus 439 

" 34. Apparatus of Monnier and Auriol 44^ 

'* 35. McGowan's apparatus for the iodometric estimation of nitric acid.... 451 

" 36. Apparatus of Gooch and Gruener 454 

*' 37. Apparatus of Chabrier 475 

" 38. Schaeffer's nitrous acid method 47^ 

" 39. Water distilling apparatus, Bureau of Chemistry 482 

Plate, figure 40. Scene showing mining operation opposite 490 

Plate, figure 41. Drilling in potash mine preparatory to blasting opposite 490 

Plate, figure 42. Scene during lunch hour in a potash mine opposite 490 

Figure 43. Geological relations of the potash deposits near Stassfurt 507 

44. Diagram showing law of crystallization of potash salts 511 

45. Graphic representation of theory of crystallization 513 

" 46. Graphic representation of the deposition of different salts 514 

" 47. Apparatus for making pure chlorplatinic acid 57^ 







EXAMINATION OF FERTILIZING MATERIALS, 
FERTILIZERS, AND MANURE 



PART FIRST 



DEFINITIONS, SAMPLING AND PRELIMINARY TREATMENT 

1. Introduction.— The principal plant foods occurring in soils 
are named and the methods of estimating them described in the 
first volume. As fertiHzers are classed those materials which 
are added to soils to supply deficiencies in plant foods or to render 
more available the stores already present. There is little difference 
between the terms fertilizer and manure. In common language 
the former is applied to materials prepared for the farmer by 
the manufacturer or mixer, while the latter is applied to those 
accumulated about the stables or made elsewhere on the farm. 
Thus it is common to speak of a barn-yard or stall manure and of 
a commercial fertilizer. This distinction is more nominal than 
real. If a choice is to be made between terms, manure is pref- 
erable. The term fertilization, moreover, is applied biologically 
to the effective congress of the male and female elements of the 
tgg, and thus confusion may arise by the application of that term 
to any process of manuring. 

In harmony with the common practice in this country, however, 
the words will be used in this volume in the sense indicated above. 

One of the objects of the analysis of soils is to determine the 
character of the fertilizer which should be added to a field in 
order to secure its maximum fertility. 

One purpose of the present manual is to determine the fitness 
of offered fertilizing material to supply the deficiencies which may 
be revealed by a proper study of the needs of the soil. 

2. Occurrence of Fertilizers in Nature. — In the succession of 
geological epochs which has marked the natural history of the 
earth there have been brought together in deposits of greater or 
less magnitude the stores of plant food unused by growing crops 



AGRICULTURAL ANALYSIS 

or which may once have been part of vegetable and animal organ- 

""For a full description of the extent and origin of these deposits 
the reader is referred to works on economic geology. A bnc 
description of them is given further on ni connection with the 
l^ilizing materials which they furnish. These deposits are h 
chief soiirces of the commercial fertilizers of a rninera nature 
which are offered to the farmers of to-day and to which the agri- 
cultural analyst is called upon to devote much of his time an. 
labor The methods of determining the chemical composition and 
agricultural value of these deposits, as practiced by the leading 
chemists of this country and Europe, will be fully set forth in the 

following pages. , 

, Waste Matters as Fertilizing Materials.-In addition to the 
natural products just mentioned, the analyst will be called on also 
to deal with a great varietv of waste materials which, in the last 
few years, have been saved from the debris of factories, abattoirs 
and other sources and prepared for use on the farm. Among 
these waste matters mav be mentioned bones, horns, hoofs hair, 
tankage, dried blood, f^sh scrap, oil cakes, ashes, sewage and sew- 
age precipitates, offal of all kinds, leather scraps, and organic 

debris in general. ■ ,, i 

It is important, before beginning an analysis, and especially be- 
fore passing a final judgment on the data obtained, to know the 
origin of the substances to be determined. As has already been 
pointed out in the first volume, the process which would be ac- 
curate with a substance of a mineral origin might lead to error 
if applied to the same element in organic combination. This is 
particularly true of phosphorus and potash. A simple micro- 
scopic examination will usually enable the analyst to determine 
the nature of the sample. In this manner, in the case of a phos- 
phate it would at once be determined whether it is derived from 
bone,' mineral, or basic slag. The odor, color and general con- 
sistence will also aid in the determination. 

4 Valuation of Fertilizing Ingredients.— Perhaps there are no 
more numerous and perplexing questions propounded to the 
analvst than those which relate to the value of fertilizing materials. 






TRADE VALUES OF FERTILIZING INGREDIENTS 3 

There is none harder to answer. As a rule, these questions are 
asked by the farmer, and refer to the money value of the fertil- 
izers put on his fields. In such cases the cost of transportation is 
an important factor in the answer. The farther the farmer is re- 
moved from the place of fertilizer manufacture the greater, as a 
rule, will be the cost. Whether the transportation is over land or 
l)y water also plays an important part in the final cost. The dis- 
covery of new stores of fertilizing materials has also much to do 
with the price. This fact is especially noticeable in this country, 
where the price of crude phosphates at the mines has fallen in a 
few years from nearly six dollars to three dollars per ton.^ 

This decrease has been largely due to discoveries of vast beds 
of phosphatic deposits in Florida, North Carolina, Tennessee and 
Wyoming. The state of trade, magnitude of crops and the vigor 
of commerce also afTect, in a marked degree, the cost of the raw 
materials of commercial fertilizers. 

Since 1904 there has been some improvement in prices, as is 
seen by the data on the following page. 

5. Trade Values of Fertilizing Ingredients in Raw Materials and 
Chemicals. — As has already been mentioned, the task of fixing a 
money value for fertilizer ingredients is dif^cult. In fact, it is a 
very general opinion that such values should be left to the usual 
mandates of trade and the function of the analyst should cease 
when he has disclosed the character and amount of each in- 
gredient of commercial value. The market price is then regulated 
by the ordinary conditions of demand, supply and transportation. 
In some cases the law^s of the State require the construction of a 
table showing the money value of each of the component parts, 
in such a case the analyst is guided by trade conditions and fur- 
ther by the character or origin of the material in question. Thus 
soluble phosphoric acid is far more valuable than the insoluble 
variety, and nitrogen in the form of blood or saltpeter than nitro- 
gen in horns, hoofs or hair. 

The values proposed for 1907 by the Massachusetts experiment 
station are given below. ^ 

* The American Fertilizer, 1905, 22 : 17. 

* Mas.^achusetts Experiment Station, 1907, Bulletin 119:16. 



I 

i 



A AGRICULTURAL ANALYSIS 

4 

Cents per pound 

,, 17-5 

Nitrogen in ammonia salts ^^ 

«« " nitrates !'/ ' \ J 

Organic nitrogen in dry and fine-ground fish, nieat, blood, and 

in high-grade mixed fertilizers 20.5 

« 4i «< fine-ground bone and tankage y 20.5 

t< «« " coarse bone and tankage ^S-O 

Phosphoric acid soluble in water 5-o 

soluble in ammonium citrate 4-5 

** «* in fine-ground fish bone and tankage 4-o 

li ♦< in coarse fish bone and tankage 3-o 

«' in cottonseed meal, castor pomace, and wood 

ashes ' ' " ' ^' 

" insoluble (in water and in neutral ammonium 

citrate) in mixed fertilizers 2.0 

Potash as sulfate, free from chlorids 5-o 

" as muriate, (chlorid) "J"^^ 

, , 8.0 

" as carbonate 

The above schedtile of trade values is adopted by Massachu- 
setts Connectictit, Rhode Island, Maine, Vermont, New York 
and New Jersey. It is based on the current market prices in 
ton lots of the materials. 

The values assigned by the Maryland station differ but shghtly 

f rom the above.^ . 

Cents per pound 

In mixed fertilizers: 

' 20.0 

For nitrogen as ammonia 

" potash (K2O) free of chlorids ^-^ 

" '• (K.,0) as chlorid or in kainit 5-o 

'' phosphoric acid soluble in water and ammonium citrate ... 5.0 

♦ ' insoluble phosphoric acid ^-^ 

t, 44 »» '• from rock phosphate i-o 

In dissolved rock: 

For phosphoric acid soluble m water and ammonium citrate. • • 4-5 

In ground bone: 

For nitrogen as ammonia in fine bone ^^-^ 

4. 4» <^ " «' " medium ))one i5-0 

«« " in medium bone ^4-0 

«« " " coarse bone ^3*^ 

' ' phosphoric acid in fine bone 5-o 

44 44 •«♦ »« *' medium bone 45 

. 44 «t «* «« niedium bone 40 

4 4 «« 44 44 coarse bone 2.0 

In tankage and ground fish : 

For nitrogen as ammonia ^5 o 

" phosphoric acid 3-o 

3 The Maryland Agricultural College (Quarterly, 1907, No. 37 : 3- 



II 






DIRECTIONS 5 

The organic nitrogen in superphosphates, special manures and 
mixed fertilizers of a high grade is usually valued at tlie highest 
figures laid down in the trade values of fertilizing ingredients in 
raw materials; namely, eighteen and one-half cents per pound, it 
being assumed that the organic nitrogen is derived from the best 
sources, viz., animal matter, as meat, blood, bones or other equally 
good forms, and not from leather, shoddy, hair or any low priced, 
inferior form of vegetable matter, unless the contrary is evident. 
In such materials the insoluble phosphoric acid is not given any 
Talue or only a mere trifle per pound. These values change as 
the markets vary. 

The scheme of valuation prepared by the Massachusetts station 
does not include phosphoric acid in basic slags. By many experi- 
menters the value of the acid in this combination, tetracalcium 
phosphate, is fully equal to that in superphosphates soluble in 
water and ammonium citrate. It would perhaps be safe to assign 
that value to all the phosphoric acid in basic slags soluble in a 
five per cent, citric acid solution. 

Untreated fine-ground phosphates, especially of the soft variety 
so abundant in many parts of Florida, have also a high manurial 
value when applied to soils of an acid nature or rich in humus. 
On other soils of a sandy nature, or rich in calcium carbonate, 
such a fertilizer would have little value. The analyst in giving an 
opinion respecting the commercial value of a fertilizer must be 
guided not only by the source of the material, its fineness or 
state of decomposition, and its general physical qualities, btit also 
by the nature of the crop which it is to nourish and the kind of 
soil to which it is to be applied. 

GENERAL PRINCIPLES OF SAMPLING 
6. Directions. — It is impracticable to give definite directions for 
getting samples of fertilizers which will be applicable to all kinds 
of material and in all circumstances. If the chemist himself have 
cliarge of the sampling it will probably be sufficient to say that it 
should accurately represent the total mass of material at hand. 
Generally the samples which are brought to the chemist have been 
procured without his advice or direction, and he is simply called 
upon to make an analysis of them as they are presented. 



AGRICUI.TURAI, ANALYSIS 



7. General Principles of Sampling. — The report of the chairmaii 
of the committee charged with presenting to the Sixth Interna- 
tional Congress at Rome the principles of sampling and sugges- 
tions in respect of the method in which they should he carried 
out contains the following directions.* 

The subject of sampHng for analysis may be very properly 
divided into a general and a special part. I therefore shall dis- 
cuss the problem in this way : First, with a brief statement of the 
general principles which should underlie sampling, followed by 
some special observations on sampling in special cases. 

8. Object of Sampling. — The object of securing a sample for 
analysis is self-evident ; namely, that the sample should repre- 
sent exactly, or as nearly as possible, the mean composition of the 
whole deposit or substance from which it has been separated. 
For this reason, much must be left in all cases to the sound 
judgment of the person in charge of the sampling. This per- 
son, whenever possible, should be the analyst himself, as no one 
can judge so well as the one who is called upon to do the analyt- 
ical work the character of the sample necessary to' secure a 
proper material on wdiich the analysis is to be conducted. There- 
fore, it is almost mipossible to lay down any general principles 
which should guide the expert in securing the sample of his 
material unless the character of that material be known. 

9. Classes of Materials. — The materials which are to be oper- 
ated upon by the analyst are naturally divided into three states, 
namely, gaseous, liquid and solid. These bodies pass gradually 
from one state to another, and especially is this true of those 
passing from a solid to a liquid condition. The transition from 
the liquid to the gaseous form is very sharp and well defined. 

10. Sampling a Gas. — In general, in the sampling of a 
gaseous material it is only necessary that the gaseous contents of 
the vessel, room or space should be thoroughly mixed in order 
that any given portion of the gas may represent the whole sample. 
This is especially true if the gases be of a mixed character or of 
different specific gravities. Where, for instance, carbon dioxid 

* \Viley, Methods of Sampling Materials for Analysis, Atti del VI Con- 
gresso internazionale di Chiiiiica applicata, 1907, 7 : 170. 



SAMPLING A LIQUID 



is generated in the lower part of a room filled with air, being a 
heavier gas it would naturally accumulate as a heavy liquid would 
accumulate under a lighter one. A sample of the gas, therefore, 
in a confined space of this kind would not be representative of the 
whole contents unless previous to the sampling the whole were 
subjected to violent stirring. An ordinary electric fan properly 
placed in a room will within a short time so thoroughly mix its 
gaseous contents that a sample may be drawn which will repre- 
sent fully the character of the whole. 

In order that a sample of the gas may be unmixed and un- 
absorbed, it is w^ell that it should be aspirated into a vessel filled 
with a liquid with which the gas is not miscible. Mercury, of 
course, is the best liquid for this purpose for most gases, but on 
account of its great weight and cost is unsuitable. As a rule, 
water will be found entirely satisfactory for the aspirating mate- 
rial, especially if the vessel be of considerable size so that the total 
volume of gas drawn in is rather large. The small quantity of 
gas which will be absorbed may be practically neglected. 

A very good sample of gas may also be secured by pumping 
gas from any room or confined space into a dry rubber bag which 
i.=; previously completely flattened out so as to expel any air which 
it may contain. In order that the last traces of air may be ex- 
pelled, it is advisable in a case of this kind to fill the rubber bag 
at least partially full of gas, remove it from the room where the 
sampling is made, and express the contents, then carry back into 
the room and refill. 

Gases may also be sampled into eudiometers or other vessels in 
which the analytical processes are to be carried out. In all these 
cases the study of the nature of the case, the experience of the 
analyst and the character of the analysis wall determine the meth- 
ods which are best adapted to the purpose. 

II. Sampling a Liquid. — The sampling of liquid bodies is to be 
accomplished in the same general way. A* thorough stirring 
of the liquid should always precede the sampling in order that 
the sample may ])e uniform in character. The stirring may 
be made either by mechanical means, as usually practiced, or, 
if the liquid be one which does not contain a large amount of 



8 



AGRICULTURAL ANALYSIS 



gas, pure air may be blown through it. The mechanical method 
by paddles or other stirrers, however, is to be preferred when 
it' can be practiced. The sampling of water for analytical pur- 
poses requires special methods which will be given later. 

12. Sampling a Solid.— The general principles which should 
underlie and regulate the sampling of solid materials are 
more difficult to enunciate. Here we have the greatest variety of 
conditions. Solid materials may be of such a character that they 
may be easily mixed ; as, for instance, in the case of a powder or 
any substance in a finely subdivided state. On the other hand, a 
material from which a sample is to be taken may be solid, ex- 
tremely hard and difficult of disintegration, as is the case with a 
rock or a piece of metal or of wood. The difficulties which ob- 
tain, therefore, are very great in this class of bodies and require 
special precautions, great experience and knowledge of the sub- 
ject and the exercise of patience in order that good results may be 
secured. Where bodies can be perforated— as in the case of wood 
— very good samples may be taken by means of augers which are 
made to penetrate the wood at different places, and thus a sam- 
ple secured. If the material is contained in bags or barreh 
which are easily penetrated, the ordinary trier which is used for 
sampling is, as a rule, sufficient to give an average sample. In the 
case of metal, boring may be practiced with a small drill and rea- 
sonably satisfactory samples secured. 

The local conditions which obtain, the character, size and shape 
of the body, the facilities at hand for sampling, the purpose for 
which the analysis is to be made, and the general environment will 
be sufficient to guide the expert analyst in his work and enable 
him to get a sample of material which to him is a reasonably sat- 
isfactory representative. In a little more general way it may be 
said in regard to liquids which are supposed to have been mixed 
at one time and which have been barreled or bottled — as in the 
case of wine, vinegar or beer — it is always advisable to take a 
portion of the sample from each package. Solids which are finely 
divided and evenly mixed according to a uniform standard and 
which have been taken from a single source, as, for instance, in 
the case of fertilizers which are contained in bags, shoukl have at 



1 1 



SUBDIVISION OF SAMPLE 9 

least a sample taken from every tenth bag. If there are less 
tlian ten bags, however, not less than three or four of the bags 
should be sampled. 

In regard to the preservation of samples after they are secured, 
ordinary fruit jars which are furnished with rubber gaskets may 
be used for liquids without any fear of loss. In the case of liquids, 
where a narrow-necked receptacle is employed, and especially 
where it is necessary or advisable to secure a small volume of 
sample, a bottle which is closed with a rubber stopper may be 
used. A cork stopper which has been coated with paraffin and 
afterwards secured with sealing wax may be substituted some- 
times to advantage for a rubber stopper. Of course, in many 
cases the presence of paraffin is objectionable, and in such cases 
it should not be used. 

13. Subdivision of Sample. — The extent of the subdivision 
of the sample depends entirely on its nature and the 
character of the examinations to be made. In general 
it may be said that the finer the subdivision the better 
the analytical results. When substances are dry and can be easily 
pulverized, they should be powdered and passed through a sieve 
with a millimeter or, better still, a half millimeter mesh. The 
sample may be selected advantageously from a large amount of 
material by repeated quartering, the subsamples being passed suc- 
cessively through the crusher from time to time so as to have only 
a small amount of the sample in a fine state of subdivision when 
the final grinding occurs. In the case of a tough and difficultly 
reduced substance like meat, as large a quantity as possible should 
be passed repeatedly through a sausage mill, mixing the whole 
at once for each grinding, quartering the residue and rcgrinding, 
and mixing the subsamples. 

Many products which consist of relatively small particles which 
can not be ground may be thoroughly mixed together and sub- 
divided by means of quartering until a sample of proper size is 
obtained. If this material is soluble in water, the whole of the 
sample may be weighed, dissolved in water and an aliquot por- 
tion of the mixture taken for analysis. If soluble in other solvents 
than water, a similar process is to be employed. It appears that 



it 



lO 



AGRICULTURAL ANALYSIS 



the complete mixture of many substances which are soluble and 
which are of such a nature that they can not be readily ground is 
best effected by dissolving them in water or some other satisfac- 
tory solvent, mixing the solution and taking an aliquot part there- 
of, as above suggested. 

If liquids have solids in suspension it is often necessary to thor- 
oughly mix them in order that the sample may contain its pro- 
portionate part of the solid matters. Milk may be sufficiently 
mixed by pouring several times from one receptacle to another 
before the sample is removed. Carbonated liquids may be with- 
drawn from the casks or bottles in which they are held by means 
of a spiggot with a stop-cock. In the case of viscous substances 
a large spatula, cheese-knife or cheese-sampler may be con- 
veniently employed. For instance, this method of sampling may 
be practised with a substance like massecuite. In case the degree 
of fluidity is too great to admit of such a method of sampling, a 
slotted tube may be used which is inserted in the semi-liquid mass 
until filled and then withdrawn and its contents removed for the 
sample. Sirups and molasses in which the sugar has been par- 
tially crystallized offer unusual difficulties in sampling, owing to 
the great difficulty of breaking u]) the crystals and mixing them 
uniformly with the liquid portions. In such cases it is better to 
dissolve the crystals if possible by gentle heating and stirring of 
the products, or even the addition of a known amount of water 
until the whole of the crystallized portions are dissolved. 

There are some plastic materials which it is almost impossible 
to sample in a uniform way. In these cases it may be found neces- 
sary to subdivide the material by cutting a selected and occasional 
piece representing, as nearly as possible, the whole material. 
Materials like street sweepings and garbage may be sampled 
when they are loaded or unloaded by taking an occasional shovel- 
ful and throwing it off to itself, until a carload or other large 
quantity has thus been sampled. These materials which are re- 
moved may then be thoroughly mixed together and resampled in 
the same way. 

Sugar-cane and sugar-beets may be sampled by taking at ran- 
dom every tenth or hundredth beet or cane. The same is true 



SAMPLING OF FERTILIZERS 



II 



of apples and other fruits. In such sampling care must be exer- 
cised not to select the particular individual to be sampled, but to 
take every one which comes within the prescribed limit. In 
general, it may be said that it would be advisable to divide the 
materials which are the usual subjects of analysis into different 
classes and subdivisions, and that uniform methods for these 
classes and subdivisions be recommended. 

14. Sampling of Fertilizers.— Perhaps there are no more numer- 
ous and perplexing questions connected with the subject of 
sampling than those which arise in the case of fertilizers. In 
many countries the method of sampling the fertilizing materials 
is prescribed by law. It is impracticable to give definite direc- 
tions in all cases which will be applicable to all kinds of materials 
and in all instances. The chemist himself having charge of secur- 
ing the sample should see that it accurately represents the total 
amount of the material sampled. Too often the samples which 
are brought to the chemist have been secured without his advice or 
direction and really are not representative. 

For sampling manufactured fertilizers, which in this country 
are usually very finely divided, I have found nothing better than 
a slotted brass tube. The tube may be from i to i>4 inches in 
diameter, with a half or three-quarter inch slot. It should be 
long enough to reach the full length of the package, and the lower 
end should be provided with a cutting edge that it may be forced 
into the package easily. For a handle a smaller tube 3 to 4 inches 
long is brazed at right angles to the upper end of the larger tube. 
In sampling, the package of fertilizer is thrown on the side, and 
if the contents are hard they are broken up by rolling and by 
blows on the container. The slotted tube is now forced into the 
package with the slot down, turned over, shaken slightly to fill 
the tube, withdrawn, and the content emptied on a rubber or oil 
cloth. Samples are drawn from at least five per cent, of the pack- 
ages, but should always be drawn from at least three packages. 
These samples are thoroughly mixed on the cloth, a subsample 
secured by quartering, placed in a screw-top can and labeled 
for identification. This instrument and method are suitable for 
sampling all finely ground fertilizers and fertilizer materials, but 



12 



AGRICULTURAL ANALYSIS 



MIXED FERTILIZERS 



13 



f tB 



are not suitable for raw phosphate rock, coarse raw tankage, fisi. 
scrap farm manures, tobacco stems, unground kamit, nor for 
very hmipy nitrate of soda and sulfate of ammonia, all of which, 
except when mechanical devices are used, leave much to the judg- 
ment of the sampler, and for which only general instructions can 

be given. ^ 

Large samples should be secured from five to ten per cent, of 
the material, being careful to maintain the proper relation between 
the coarse and f^ne portions, and to protect the sample from loss 
or absorption of moisture. When the material is very wet, as fish 
scrap or may take up much moisture, as sulfate of ammonia, 
the sample should be weighed and brought into an air-dry condi- 
tion and again weighed. It is now coarsely ground, thoroughly 




Fig. I. Apparatiis for Crushing Mineral Fertilizers. 

mixed and a subsample taken, which may be again ground and 
subsampled if necessary. The loss or gain in bringing to an air- 
dry condition must be carefully noted and the results of the 
analysis corrected thereby. 

15. Minerals Containing Fertilizing Materials.— When possible, 
the samples should be accompanied by a description of the mines 
where they are procured and a statement of the geologic condi- 



1 



'.« 









tions in which the deposits were made. As large a quantity of the 
material as can be conveniently obtained and transported should 
be secured. Where a large quantity of mineral matter is at hand 
ii should first be put through a crusher. Many forms of crusher, 
driven by hand and other power, are on the market. They are all 
constructed essentially on the same principle, the pieces of mineral 
being broken into small fragments between two heavy vibrating 
steel plates. The general form of these crushers is seen in Fig. i. 
The fragments coming from the crusher can be reduced to a 
coarse powder by means of the iron plate and crusher shown in 

Fig. 2. 

Where only a small quantity of mineral is at hand the appa- 
ratus just mentioned may be used at once after breaking the 
sample into small fragments by means of a hammer. 

Finally the sample, if to be dissolved in an acid for sol- 
uble materials only, is reduced to a powder in an iron mortar 
until it will pass a sieve with a one, or, better, one-half millimeter 




Fig. 2. Plate Grinder for Minerals. 

circular mesh. The powder thus obtained must be stirred with 
a magnet to remove all iron particles that may have been incor- 
porated with the mass by abrasion of the instruments employed. 

If a complete mineral analysis of the sample is to be secured, 
the material freed from iron, as above described, is to be rubbed 
to an impalpable powder in an agate mortar. 

16. Mixed Fertilizers. — In securing a sample of mixed fertiliz- 
ers the first requisite is that they should be homogeneous. If a part 
of one kind of a fertilizer be in excess in any part of tlie whole, 



14 



AGRICULTURAL ANALYSIS 



the sample is apt to be nonrepresentative. The finer the materials 
in the original state and the more thoroughly they have been 
mixed the better the sample will be. If the materials be in bags 
it will be sufficient to take portions from every tenth bag or from 
three or four of the bags if there be less than ten, by means of an 
ordinary trier which is thrust through the bag and filled with the 
material therein contained. This consists of a long metal im- 
plement such as would be formed by a longitudinal section of a 
tube. The end is pointed and suited for penetrating into the 
sack and the materials contained therein. On withdrawing it, 
the semi-circular concavity is found filled with the material 
sampled. Samples in this way are removed from various parts 
of the bag and these samples well mixed together and a sub- 
sample of the amount necessary for the laboratory is then ob- 
tained. Quite a great deal more of the sample should be secured 
than is necessary for the analysis and this quantity may be 
called the "Industrial Sample." When the industrial sample, 
more or less voluminous, reaches the laboratory, the chemist is to 
begin by taking a note of the marks, labels and descriptions found 
thereon, and of the nature and state of the package which con- 
tains it and the date of its arrival. All this information should 
be entered upon the laboratory book and afterwards transcribed 
on the paper containing the results of the analysis, as well as the 
name of the person sending it. This having been done, the sam- 
ple is to be properly prepared in order that a portion may be 
taken representing the mean composition of the whole. 

If it is in a state of fine powder, such as ground phosphates 
and certain other fertilizers, it is sufficient to pass it two or three 
times through a sieve with meshes one millimeter in diameter, 
taking care to break up the material each time in order to mix 
it and to pulverize the fragments which the sieve retains. The 
whole is afterwards spread in a thin layer upon a large sheet 
of paper and a portion is taken here and there upon the point of 
a knife until about twenty grams are removed, and from this 
the portion subjected to analysis is afterwards taken. 

If the sample comes in fragments, more or less voluminous, 
such as phosphatic rocks or coarsely pulverized guanos contain- 



MIXED FERTILIZERS 



15 



ing agglomerated particles, it is necessary first to reduce the 
whole to powder by rubbing it in a mortar or by using a small 
drug mill. It is next passed through a sieve of the size men- 
tioned above and that which remains upon the sieve pulverized 
anew until all has passed through. This precaution is very im- 
portant, since the parts which resist the action of the pestle most 
liave often a composition different from those which are easily 
broken. 

When the products to be analyzed contain organic materials, 
such as horn, flesh, dry blood, etc., the pulverization is often a 
long and difficult process, and results in a certain degree of heat- 
ing, which drives off some of the moisture in such a way that the 
pulverized product is at the last drier, and, consequently, richer 
than the primitive sample. It is important to take account of this 
desiccation, and since the pulverization of a mass so voluminous 
can not be made without loss, the determination of the total weight 
of the sample before and after pulverization does not give exact 
results. In such a case it is indispensable to determine the mois- 
ture both before and after pulverizing, and to calculate the analyt- 
ical results obtained upon the pulverized sample back to the orig- 
inal sample. In order to escape this necessity, as well as the diffi- 
culties resulting from the variations in moisture during transpor- 
tation, some chemists have thought it better to always dry the 
commercial products before submitting them to analysis, and to 
report their results in the dry state, accompanied by a determina- 
tion of the moisture, leaving thus to the one interested the labor 
of calculating the richness in the normal state, that is to say, in 
the real state in which the merchandise was delivered. 

In addition to the fact that this method allows numerous 
chances of errors, many substances undergoing important changes 
in their composition by drying alone, it has been productive of 
the most serious consequences. The sellers have placed their 
wares on the market with the analysis of the material in a dry 
state, and a great number of purchasers have not perceived the 
fraud concealed under this expression so innocent in appearance. 
It is thus that there has been met with in the markets guano con- 
taining twenty-five per cent, of water, which was guaranteed to 



i6 



AGRICULTURAL ANALYSIS 



METHOD OF FRENCH SUGAR CHEiMISTS 



17 



ifi 



contain twelve per cent, of phosphoric acid, when in reahty it con- 
tained only eight per cent, in the moist state. 

17. Barn- Yard Manures. — The sampling of stall and barn-yard 
manures is more difficult on account of the fact that the materials 
are not homogeneous and that they are usually mixed with straw 
and other debris from the feed trough, and only the greatest care 
and patience will enable the operator to secure a fair sample. 

In the case of liquid manures the liquid should be thoroughly 
stirred before the sample is taken. In a given case the difficulty 
of securing representative samples of stall manure is described 
and also methods of removing it.^ The stall manure sampled had 
been piled in the cattle-yard for a time and the cattle were al- 
lowed to run over the heaps for an hour or two each day. Pigs 
were allowed free access to the heaps in order to insure a more 
perfect mixture of the ingredients. 

Twenty-nine loads of 3000 pounds each were sampled from the 
exposed heap and 34 loads of 2000 pounds each were sampled 
from the covered heap. From each load were removed 
two carefully selected portions of 10 pounds each, which 
were placed in separate covered boxes numbered A and B. When 
the sampling was completed these boxes were covered. After 
being removed to the laboratory the boxes w^ere weighed and the 
contents thoroughly mixed. Two samples of 12 liters each 
were drawn from each box. One-third of this was chopped in 
a large meat chopper and the other two-thirds taken into the 
laboratory without being cut. These samples, on entering the 
laboratory, were weighed and dried at a temperature of 60° to 
secure the samples for analysis. 

18. Sampling of Materials Used for Road Building. — The mate- 
rials of which roads are built, especially the rock materials, have 
of late years been subjected to careful scientific examination. 
The methods may be applied also to minerals containing fertilizer 
ingredients. In the examination of rocks and rock materials 
Avhich are used to build roads, the sample which is sent should 
be large enough to give assurance that it practically represents 
the materials employed. For this purpose not less than 30 pounds 

^ Proceedings i2tli and 13th Meetings of the Society for the Promotion 
of Atrricultural Science, 1 891-2 : 139. 



^ 



of the sample should be secured. If there seems to be any reason- 
able doubt regarding the character of the sample, its source 
should be investigated and a proper sample secured. In general, 
the principles which should guide the securing of samples of 
this kind of material are those which are in vogue for ordinary 
mineral analyses, save the larger quantity of road material which 
, is usually required. 

19. Absence of Official Methods.— Although the proper study of 
a fertilizer has its chief economic value when the analysis is con- 
ducted on a representative sample, the official chemists have given 
but scant attention to the subject of sampling. It is evident that 
a detailed description of the procedure to be followed in each 
case would be practically impossible. In such a variety of com- 
pounds as is presented by fertilizing materials and fertilizers, and 
especially manures, the good judgment of the chemist in charge of 
the sample must point the way to securing reasonably satisfactory 
results. Patience and ingenuity will lead to the solution of the 
most intricate problems which may arise. 

20. Method of the French Experiment Stations. — In the method 
employed by the French experiment stations, it is directed that 
in no case should stones or other foreign particles be removed from 
the fertilizer sampled, but they should enter into the sample 
in, as nearly as possible, the same proportions as they exist in 
the whole mass. 

In the case of stones or other solid masses which are to be 
sampled, as many portions as possible should be taken from all 
parts of the heap and these should be reduced to a coarse powder, 
thoroughly mixed together and sampled. 

In case the material is in the form of a paste, if it is homo- 
geneous, it will be sufficient to mix it well ; but in case there is a 
tendency for the pasty mass to separate into two parts, of which 
the one is a liquid and the other more of a solid consistence, 
it may be well to get samples from each in case they can not be 
thorotighly incorporated by stirring. 

21. Method of the French Association of Sugar Chemists. — The 
method adopted by the French sugar chemists directs that the 
sampling should begin with the fertilizer in bulk or from a portion 



i8 



AGRICULTURAL ANALYSIS 



PREPARATION OF SAMPLE IN LABORATORY 



19 



used for industrial purposes. The part for analysis is to be taken 
from the above sample after it has been sent to the laboratory.. 
The method of procedure should be varied according to the con- 
dition of the substances to be analyzed. 

The large sample selected from the goods delivered to com- 
merce having been delivered at the laboratory, the analytical 
sample is obtained as described in 16. 

22. Method of the International Congress of Applied Chemistry. 
—The committee designated by the Fifth International Congress 
of Applied Chemistry has formulated the following general 
principles of sampling fertilizers and component materials there- 

of.« 

1. Samples not drawn in accordance with these regulations are 
to be refused by official analysts, such refusal being recorded on 
the certificate. 

2. Samples are only to be considered as properly identified, if 
drawn during unloading on railway or quay, in the presence of 
representatives of both parties, or by a sworn sampler, and in ac- 
cordance with these regulations. 

3. In the case of manufactured products, a sample is to be 
secured by means of a sampling iron from every tenth bag, or if 
the material is in bulk, from at least ten different places through- 
out the parcel. 

4. In the case of shiploads of raw materials every fiftieth bag or 
bucketful during discharge (corresponding to two per cent, ot 
the whole) is to be set aside, and from this, after first crushing to 
at least the size of a hazel-nut, a sample is to be removed for the 
determination of moisture ; a further sample for the determination 
of the constituents of value is to be obtained in the same way as in 
the case of manufactured products after the sample has been re- 
duced to a fine state by grinding and sifting. 

5. The samples — in weight about 300 grams — are to be filled 
loosely into strong, clean and absolutely dry glass bottles. 

6. At least three samples are to be prepared. The bottles are to 
be hermetically closed and sealed by the persons conducting the 
sampling. 

« Fiinfter, Iiiternationaler Kongress fiir aiigewandte Chemie, Bericht, 
1904, 4. :937. 





7. The labels are to be signed by the persons supervising the 
sampling and are to be attached by means of the wax used in 
sealing the bottles. 

8. The samples are to be kept in a cool, dark and dry place. 

9. Materials of heterogeneous composition must be sufficiently 
reduced in size and mixed before bottling. 

23. Influence of State of Subdivision. — The importance of good 
sampling in securing reliable analytical data is shown by Riviere 
by comparing the results of analysis of samples from different 
parts of the same bulk material."^ The substance examined was 
dried blood. A sample received from a farmer was 
passed as customary through a mill and contained 9.95 
per cent, of nitrogen. This being lower than the guar- 
anty, led to asking for a new sample of not less than 
500 grams. In this sample there were found 11.20 per cent, of ni- 
trogen. The sample was then divided into two portions by means 
of a sieve. The fine part, 204 grams, contained 9.40 per cent, of 
nitrogen and the coarse part 12.10 per cent. The two portions were 
again mixed and a sample analyzed contained 11. 14 per cent, of 
nitrogen. It is evident from the above data that in transportation 
the fine particles tend to go to the bottom and the large to be col- 
lected on the top of the mass so that even were it well mixed at 
the start, at the end of the journey samples from different parts 
would show varying contents of nitrogen. 

24. Preparation of Sample in Laboratory. — Tlie method of 
preparing mineral fertilizers for analysis has been given under 
the directions for sampling. Many difficulties attend the proper 
preparation of other samples, and the best approved methods of 
procedure are given below. 

According to the directions given by the Association of Offi- 
cial Agricultural Chemists the sample should be well intermixed, 
finely ground, and passed through a sieve having circular per- 
forations one millimeter in diameter.^ The processes of grind- 
ing and sifting should take place as rapidly as possible so that 
there may be no gain or loss of moisture during the operation. 

' L'Engrais, 1905, 20 : 233. 

* Division of Chemistry, Bulletin 46, Revised, 1899 : 11. 



' I 



20 



AGRICULTURAL ANALYSIS 



GERMAN METHOD 



21 



li 



25 Method of the International Commission.-The methods 
adopted by the international commission are as follows : 

(a) Dry samples of phosphates or other artific.al manures may 

be simply sifted and then mixed. 

(bHn the case of damp materials, where the above procedure 
is not possible, the preparation must be confined to a careful mix- 

'"%Y I'^'the case of raw phosphates and a.iimal charcoal, a water 
determination is to be made, as confirmatory evidence. 

(d) In dealing with substances which are apt to lose wate 
du hi grinding, the moisture is to be determined both before and 
' r the preparation of the sample, the results o -the analysis 
being afterwards calculated back into the original hygroscopic 
condition of the sample as received. 

fe Method of the French Agricultural Stations.-l he man- 
ne of proceeding recommended by the French st^^ons varies 
with the fertilizer." If it is not already in the form of a 
"wderit is necessary to pulverize it as finely as possible by rub- 
bing it up in a mortar. In certain cases, as with superphos- 
ohals the material should be passed through a sieve havmg 
apertures of one millimeter diameter, all the larger parts being 
pulverized until they will pass this sieve 

When the matters are too pasty to be divided in the mortar 
thev should be divided by means of a knife or a spatula. Th y 
should then be incorporated with a known weight of >nert pul- 
ruent matter such as fine sand, with which they shoirid be 
ho oughly mixed and in subsequent calculations the quantity 
o and or other inert matter added must be taken into consid- 
eaion. Usually a pasty state of a fertilizer is due to the 
humidity of the mixture. In this case a considerable volume of 
he sample is dried and then reduced to a pulverulent state 
In the subsequent calculations, however, the percentage of mois- 
ture lost must be taken into consideration. 

Before drying a sample it is necessary to take into considera- 
tion whethe; or not the product will be modified by desiccation 
» Grandeau, Traite .1' Analyse Matiere.s des agricoles, 3rd Edition. .897, 
1 : 409- 



'A 



•■-S 

^ 






as would be the case, for instance, with superphosphates. With 
these, which are often in a state more or less agglomerated, it is 
recommended to introduce, in order to divide them, a certain 
quantity of calcium sulfate to reduce them to a pulverulent state. 
In the case of animal debris they should be divided as finely 
as possible with the aid of scissors and then passed through a 
drug mill if dry enough. They are then mixed by hand and 
may finally be obtained in a state of considerable homogeneity. 

When fertilizers are in a pasty state or more or less liquid, they 
are dried at ioo°, first introducing a little oxalic acid in case 
they contain any volatile ammoniacal compounds. The product 
of desiccation is then passed through a mill. Before treating in 
this way it is necessary to be sure that the composition will not 
be altered by drying. In the case of a mixture containing super- 
phosphates and nitrate, for instance, drying would eliminate the 
nitric acid. In such a case the free phosphoric acid should be 
neutralized with a base like lime. In the case of fertilizers con- 
taining both nitrates and volatile ammoniacal compounds, the 
addition of oxalic acid might also set free nitric acid during the 
desiccation. In such a case it is necessary to dry two samples ; 
one with the addition of oxalic acid for the purpose of estimating 
the ammonia, and the other without the acid for the purpose of 
estimating the nitrate. A qualitative analysis should precede 
all the operations so as to determine the nature of the material 
to be operated on. 

27. German Method.— In the method pursued by the German 
experiment stations the manipulation is conducted as follows •}^ 

(i) Dry samples of fertilizers must be passed through a sieve 
and afterwards well mixed. 

(2) With moist fertilizers, which can not be subjected to the 
above process, the preparation should consist in a careful and 
thorough mixing, without sieving. 

(3) On the arrival of the samples in the laboratory their 
weight should be determined. The half of the sample is pre- 
pared for analysis and the other part, to the amount, at least, of a 
kilogram, should be placed in a glass vessel, closed air-tight, and 

^•Die landwirtschaftlichen Versuchs-Stationen, 1891, 38 : 303- 



22 



AGRICULTURAl. ANALYSIS 






GENERAL OBSERVATIONS 



23 



left in a cool place for at least a quarter of a year from the time 
of its reception, in order that it may be subjected to any sub- 
sequent investigations which may be demanded. 

(4) In the case of raw phosphates and bone-black the amount 
of water which they contain should be determined at from 105° to 
110°. Samples which in drying lose ammonia in any way, should 
have this ammonia determined. 

(5) Samples which are sent to other laboratories for control 
analyses should be securely packed in air-tight glass bottles. 

(6) The weight of the samples should be entered in the 
certificates of analysis. 

(7) Samples which, on pulverizing, change their content of 
water, must have the water content estimated in both the coarse 
and powdered condition and the results of the analysis must be 
calculated to the water content of the original coarse substance. 

28. Special Cases.— Many cases arise of such a nature as to 
make it impossible to lay down any rule which can be followed 
with success. As in almost every other process in agricultural 
chemistry, the analyst in such cases must be guided by his judg- 
ment and experience. Keeping in view the main object, viz., to 
secure in a few grams of material a fair representation of large 
masses, he will generally be able to reach the required result by 
following the broad principles already outlined. In many cases 
the details of the work and the adaptations necessary to success 
must be left to his own determination. In all special cases the 
methods of securing the samples should accompany the -analytical 
data. 

DRYING SAMPLES OF FERTILIZERS 

29. Difficulties of Desiccation. — The determination of the un- 
combined moisture in a sample of fertilizer is not an easv 
task. In some cases, as in powdered minerals, drying to con- 
stant weight at the temperature of boiling water is sufficient 
In organic matters containing volatile nitrogenous and other com- 
pounds these must first be fixed by oxalic or sulfuric acid, before 
the desiccation begins. If any excess of sulfuric acid be added, 
however, drying at 100° becomes almost impossible. Particular 
precautions must be observed in drying superphosphates. In 




4 



drying samples preparatory to grinding for analysis it is best to 
stop the process as soon as the materials can be pulverized. In 
general, samples should be dried only to determine water, and 
the analytical processes should be performed on the undried ' 
portions. It is not necessary, as a rule, to dry samples of mineral 
fertilizers in an inert atmosphere, such as hydrogen or carbon 
dioxid. Drying in vacuo may be practiced when it is desired 
to secure a speedy desiccation or one at a low temperature. 

30. Official Methods.— The official agricultural chemists direct, 
in the case of potash salts, sodium nitrate, and ammonium 
sulfate, to heat from one to five grams at about 130° until the 
weight is constant.^^ The loss in weight is taken to represent the 
water. For all other fertilizers heat two grams, or five grams 
if the sample be very coarse, for five hours in a steam bath. The 
international commission prescribes heating to constant weight 
at 100°, using 10 grams of material. Substances containing gyp- 
sum are dried for three hours. Potash salts are dried in harmony 
with the regulations prescribed by the potash syndicate at 
Leopoldshall, Stassfurt. 

In the German stations in the case of untreated phosphates 
and bone-black the moisture is estimated at from 105° to 110°. 
Samples which lose ammonia should have the weight of ammonia 
given off at that temperature, determined separately. 

31. General Observations.— For purposes of comparison it would 
be far better to have all contents of moisture determined at the 
boiling point of water. While this varies with the altitude and 
barometric pressure yet it is quite certain that the loss on drying to 
constant weight at all altitudes is practically the same. Where 
the atmospheric pressure is diminished for any cause the water 
escapes all the more easily. This, practically, is a complete com- 
pensation for the diminished temperature at which water boils. 
Only in the case where free sulfuric or phosphoric acid is present 
would this method be ineffective. The highly hygroscopic nature 
of these acids in a concentrated state renders' desiccation at such a 
temperature practically impossible, in such cases a weighed ex- 
^^ Division of Chemistry, Bulletin 46, 1S99 : ii. 



24 AGRICULTURAIv ANALYSIS 

cess of base should be added to convert the acids into sulfates or 
phosphates. 

Where the samples contain no ingredient capable of attacknig 
aluminum, they can be conveniently dried, in circular dishes of 
this metal about seven centimeters in diameter and one centi- 
meter deep, to constant weight, at the temperature of boiling 
water. 

32. Moisture in Monocalcium Phosphates.— In certain fertilizers, 
especially superphosphates, containing the monocalcium salt, the 
estimation of water is a matter of extreme difficulty on account 
of the presence of free acids and of progressive changes in the 
sample due to different degrees of heat. 

•Stoklasa has studied these changes and reaches the following 
results :^- 

A chemically pure monocalcium phosphate of the following 
composition, viz., 

CaO 22-5^ P^^ ^^"^• 

PA 56.67 - - 

H,0 ^^-53" " 

was subjected to progressive dryings. The loss of water after 
10 hours was 1.83 per cent.; after 20 hours, 2.46 per cent.; 
after 30 hours, 5.21 per cent.; after 40 hours, ^6.32 per 
cent. ; after 50 hours, 6.43 per cent. The loss of water 
remained constant at 6.43 per cent. This loss represents one 
molecule of water as compared with the total molecular magni- 
tude of the mass treated. A calcium phosphate, therefore, of 
the following composition, CaH^CPO^)..^!,© loses, after 40 
hours drying at 100°, its water of crystallization. The calcium 
phosphate produced by this method forms opaque crystals which 
are not hygroscopic and which give, on analysis, the following 
numbers : 

Cg^O • 24.02 per cent. 

P.p. . . . . ... . 60.74 " 

H,o : ^5.^^ " " 

The temperature can be raised to 105° without marked change. 

1- Zeitschrift fur analytisclie Cheiiiie, 1890. 29 : 390- 



>4 



NATURAL OCCURRENCE OF PHOSPHATES 



25 



If the temperature be raised to 200° the decomposition of the 
molecule is hastened according to the following formula : 
4CaH,(POJ. = Ca.PA + Ca(P03), + CalTPA + 2H3PO, 

+ 4H,0. 
The chemical changes during the drying of monocalcium 
phosphates can be represented as follows, temperature 200° for 

one hour: 
8[CaH,(POJoH.O]==4CaH,(PO,),-fCa(P03).+Ca,P,0, 

+CaH,P,0,-f2H3PO,+ i2lLO. 
The further drying at 200° produces the following decomposi- 
tion : _ ^^ ^^ 
4CaH,(POJ.+Ca(P03).+Ca,PA+CaH,PA+2H3PO. 

=2Ca(P03)„+4CaH,P,0,+Ca,PA+2H3PO,+5H.O. 

2Ca(P03).+4CaH,P,0,+Ca,P,0;+2H3PO,= 

6Ca(PO,,)2+2CaH,PA+5H,0. 

Finally, pyrophosphate at 210° is completely decomposed into 

metaphosphate and water according to the following formula : 

6Ca(P03),+2CaH,P,0,=8Ca(P03).+2H20. 

Provided the drying is made at once at 210° the sum of the 
changes produced as indicated above, can be represented by the 

following formula : 

8[CaH,(POj2H.OJ=8Ca(P03)2+24H,0. 

The equations are to be considered as applying only to a pure 
monocalcium salt. 

MINERAL PHOSPHATES 
33 Natural Occurrence of Phosphates.— Gautier calls attention 
to the fact that the oldest phosphates are met with in the igneous 
rocks, such as basalt, trachyte, etc., and even in granite and 
-neiss ^' It is from these inorganic sources, therefore, that all 
phosphatic plant food must have been drawn. In the second order 
in age Gautier places the phosphates of hydro-mineral origin. This 
class not only embraces the crystalline apatites but also those phos- 
phates of later formation formed from hot mineral waters in the 
Jurassic, cretaceous, an-1 tertiary deposits. These deposits are 
not directly suited to nourish plants. 



13 n 



Coiiiptcs rendiis, 1893. 116 : 1271 



26 



AGRICULTURAI^ ANAI.YSIS 






m 



.'V. 



I 



i 



The third group of phosphates in order of age and assimila- 
hihty embraces the true phosphorites containing generally some 
organic matter. They are all of organic origin. 

In caves where animal remains are deposited there is an ac- 
cumulation of nitrates and phosphates. Not only do the bones 
of animals furnish phosphates but they are also formed in consid- 
erable quantities by the decomposition of substituted glycerids 
such as lecithin. The ammonia produced by the nitrification of 
the albuminoid bodies combines with the free phosphoric acid 
thus produced, forming ammonium or diammonium phosphates. 
The presence of ammonium phosphates in guanos was first noticed 
by Chevreul. 

If such dcjx)sits overlay a pervious stratum of calcium car- 
bonate, such as chalk, and are subject to leaching, a double de- 
composition takes place as the lye percolates through the chalk. 
Acid calcium phosphate and ammonium carbonate are produced. 
By further nitrification and solution the latter becomes finally 
converted into calcium nitrate. In like manner aluminum phos- 
phates are formed by the action of decomposing organic matter 
on clav. 

Davidson explains the origin of the Florida phosphates by sug- 
gesting that they arose chiefly through the influx of animals 
driven southward during the glacial period. ^^ According to his 
supposition, the waters of the ocean, during the cenozoic period, 
contained more phosphorus than at the present time. The 
waters of the ocean over Florida were shallow and the shell fish 
existing therein may have secreted phosphate as well as car- 
bonate of lime. This supposition is supported by an analysis of 
a shell of lingula oz'alis, quoted by Dana, in which there was 
^5-79 P^^ cent, of lime phosphate. In these waters were also 
many fishes of all kinds and their debris served to increase the 
amount of phosphatic material. As the land emerged from the sea 
came the great glacial epoch, driving all terrestrial animals south- 
ward. There was, therefore, a great mammal horde in the 
.swamps and estuaries of Florida. The bones of these animals 
contributed largely to the phosphatic deposits. In addition to 
^* Wyatt, Phosphates of America, 4th Edition, 1892 : 66. 



i 



NATURAL OCCURRENCE OF PHOSPHATES 



27 



this, the shallow sea contained innumerable sharks, manatees, 
whales, and other inhabitants of tropical waters, and the remains 
of these animals added to the phosphatic store. 

While these changes were taking place in the quarternary 
-.eriod, the Florida peninsula was gradually rising, and as soo!i 
as it reached a considerable height the process of denudation by 
the action of water commenced. Then there was a subsi- 
dence and the peninsula again passed under the sea and was cov- 
ered with successive layers of sand. The limestone during this 
process had been leached by rain water containing an excess of 
carbon dioxid. In this way the limestone was gradually dis- 
solved while the insoluble phosphate of lime was left in suspen- 
sion. During this time the bones of the animals before men- 
tioned by their decomposition added to the phosphate of lime 
present in the underlying strata, while some were transformed 
into fossils of phosphate of lime just as they are found to-day in 
vast quantities. 

Wyatt explains the phosphate deposits somewhat differently.^"' 
According to him, during the miocene submergence there was 
deposited upon the upper eocene limestoue, more especially in 
the cracks and fissures resulting from their drying, a soft, 
finely disintegrated calcareous sediment or mud. The estuaries 
formed during this period were swarming with animal and vege- 
table life, and from this organic life the phosphates were formed 
by decomposition and metamorphism due to the gases and acids 
with which the waters were charged. 

After the disappearance of the miocene sea there were great 
disturbances of the strata. Then followed the pliocene and ter- 
tiary periods and quarternary seas, with their deposits and drifts 
of shells, sands, clays, marls, bowlders, and other transported 
materials supervening in an era when there were great fluctua- 
tions of cold and heat. 

By reason of these disturbances the masses of the phosphate 
deposits which had not been infiltrated in the limestone became 
broken up and mingled with the other debris and were thus de- 
posited in various mounds or depressions. The general result 

^* Engineering and ISIiniiig Journal, 1890, 50 : 218. 



28 



AGRICULTURAL ANALYSIS 



NATURAL OCCURRENCE OF PHOSPHATES 



29 



of the forces which have been briefly outUned was the formation 
of bowlders, phosphatic debris, etc. Wyatt therefore classifies 
the deposits in Florida as follows : 

1. Original pockets or cavities in the limestone filled with hard 
and soft rock phosphates and debris. 

2. Mounds or beaches, rolled up on the elevated points, and 
chiefly consisting of huge bowlders of phosphate rock. 

3. Drift or disintegrated rock, covering immense areas, chiefly 
in Polk and Hillsboro counties, and underlying Peace River and 
its tributaries. 

Darton ascribes the phosphate beds of Florida to the trans- 
formation of guano.^^ According to this author, two pro- 
cesses of decomposition have taken place. One of these is 
the more or less complete replacement of the carbonate by the 
phosphate of lime. The other is a general stalactitic coating 
of phosphatic material. Darton further calls attention to the 
relation of the distribution of the phosphate deposits as affecting 
the theory of their origin, but does not find any peculiar signifi- 
cance in the restriction of these deposits to the western ridge of 
the Florida peninsula. 

As this region evidently constituted a long narrow peninsula 
■during early miocene time it is a reasonably tentative hypothe- 
sis that during this period guanos were deposited from which 
was derived the material for the phosphatization of the limestone 
either at the same time or soon after. 

Darton closes his paper by saying that the phosphate deposits 
in Florida will require careful detailed geologic exploration be- 
fore their relations and history will be fully understood. 

According to Dr. N. A. Pratt the rock or bowlder phosphate 
had its immediate origin in animal life and to his view 
the phosphate bowlder is a true fossil. He supposes the exist- 
ence of some species in former times in which the shell excreted 
was chiefly phosphate of lime. The fossil bowlder, therefore, 
becomes the remains of a huge foraminifer which had identical 
composition in its skeleton with true bone deposits or of organic 
matter. 

^^ American Journal of Science, 1S91, 41 *- 104. 




■ M 



■ Perhaps the most complete exposition of the theory of the re- 
covery of waste phosphates, with especial reference to their de- 
posit in Florida, has been given by Eldridge." He calls atten- 
tion to the universal presence of phosphates in sea water 
and to the probability that in earlier times, as durmg the 
miocene and eocene geological periods, the waters of the 
ocean contained a great deal more phosphate in solution than at 
the present time. He cites the observations of Bischof. which 
show the solubilitv of different phosphates in waters saturated 
with carbon dioxid. According to these observations apatite 
is the most insoluble form of lime phosphate, while artificial 
basic phosphate is the most soluble. Among the very soluble 
phosphates, however, are the bones of animals, both fresh and 
old Burnt bones, however, are more soluble than bones still 
containing organic matter. Not only are the organic phos- 
phates extremely soluble in water saturated with carbon dioxid, 
but also in water which contains common salt or chlorid of am- 
monium. The presence of large quantities of common salt in 
sea water would, therefore, tend to increase its power of dissolv- 
ing lime phosphates of organic origin. It is not at all incredible, 
therefore, to suppose that at some remote period the waters of 
the ocean, as indicated by these theories, were much more 
highly charged with phosphates in solution than at the present 

time. 

According to Eldridge, the formation of the hard-rock and 
soft phosphates may be ascribed to three periods : First, that in 
which the primary rock was formed ; second, that of secondary 
deposition in the' cavities of the primary rock ; third, that in 
which the deposits thus formed were broken up and the result- 
ing fragments and comminuted material were redeposited as 

they now occur. 

"The first of these stages began probably not later than the 
close of the older miocene, and within the eocene area it may 
have begun much earlier. Whether the primary phosphate re- 
sulted from a superficial and heavy deposit of soluble guanos, 
covering the limestones, or from the concentration of phosphate 
>' rreliniinary Sketch of Florida Phosphates, Author's Edition : i8. 






30 



. AGRICULTURAI. ANALYSIS 



■ 



of lime already widely and uniformly distributed throughout the 
mass of the original rock, or from both, is a difficult question. 
In any event, the evidence indicates the effect of the percolation 
of surface waters highly charged with carbonic and other acids, 
and thus enabled to carry down into the mass of the limestone 
dissolved phosphate of lime, to be redeposited under conditions 
favorable to its separation. Such conditions might have been 
brought about by the simple interchange of bases between the 
phosphate and carbonate of lime thus brought together; or by 
the lowering of the solvent power of the waters through loss of 
carbonic acid. The latter would happen whenever the acid was 
required for the solution of additional carbonate of lime, or 
when, through aeration, it should escape from the water. The 
zone of phosphate deposition was evidently one of double 
concentration, resulting from the removal of the soluble car- 
bonate thus raising the percentage of the less soluble phosphate, 
and from the acquirement of additional phosphate of lime from 
the overlying portions of the deposits. 

''The thickness of the zone of phosphatization in the eocene 
area is unknown, but it is doubtful if it was over 20 feet. 
In the miocene area the depth has been proved from the phos- 
phates in situ to have been between six and 12 feet." 

The deposits of secondary origin, according to Eldridge, 
are due chiefly to sedimentation, although some ot them may 
have been due to precipitation from water. This secondary de- 
position was kept up for a long period, until stopped by some 
climatic or geological change. The deposits of phosphates thus 
formed in the Florida peninsula are remarkably free from iron 
and aluminum in comparison with many of the phosphates of 
the West Indies. 

The third period in the genesis of the hard rock deposits em- 
braces the time of formation of the original deposits and their 
transportation and storage as they are found at the present time. 
The geological time at which this occurred is somewhat uncertain 
but it was probably during the last submergence of the peninsula. 
In all cases the peculiar formation of the Florida limestone 
must be considered. This limestone is extremely porous and' 



NATURAL OCCURRENCE OF PHOSPHATES 



31 



therefore easily penetrated by the waters of percolation. A 
^ood illustration of this is seen on the southwestern and southern 
edges of Lake Okeechobee. In following down the drainage 
canal which has been cut into the southwest shore of the lake 
the edge of the basin which is composed of this porous material 
may be seen. The appearance of the limestone would indicate 
that large portions of it have already given way to the process 
of solution. The remaining portions are extremely friable, easily 
crushed, and much of it can be removed by the ordinary 
dredging machines. Such a limestone as this is peculiarly 
suited to the accumulation of phosphatic materials due to the 
percolation of the water containing them. The solution of the 
limestone and consequent deposit of the phosphate of hme is 
•easily understood when the character of this limestone is con- 
sidered. . 

Shaler as quoted bv Eldridge in the work already referred to, 
refers to this characteristic of the limestone and says that the 
best conditions for the accumulation of valuable deposits of lime 
phosphate in residual debris appear to occur where the phos- 
phatic lime marls are of a rather soft character ; the separate beds 
having no such solidity as will resist the percolation of water 
through innumerable incipient joints such as commonly pervade 
stratified materials, even when they are of a very soft nature. 

Eldridge is also of the opinion that the remains of birds are 
not sufficient to account for the whole of the phosphatic deposits 
in Florida He ascribes them to the joint action of the remains 
of birds of land and marine animals, and to the deposition of 
the phosphatic materials in the waters in the successive subsi- 
dences of the surface below the water line. 

An important contribution to our knowledge of the origin of 
Florida phosphates has been made by Dall.- After describing the 
earlv geological epochs in the southern part of the United States, 
Dali calls attention to the abundance of foraminifera, whose shells 
form deposits of limestone, which, in southern Florida, have been 
found to be nearlv 2000 feet in thickness. 

The deposit of rocks which is known geologically as the Vicks- 

'^ The American Fertilizer, 1898, 8 108. 



9w 



n 



-2 AGRICULTURAL ANALYSIS 

burc type is composed entirely of organic material, that is, lime, 
clay, silex and iron taken up by marine animals from the water m 
which they lived and deposited as limestone. 

Toward the end of the Vicksburg epoch a movement m ele- 
vation began which brought above the sea level a part of the land 
in the vicinity of Ocala, forming an island or group of islands be- 
tween Cuba and the mainland, and the evidence is very strong 
that these low islands, containing numerous lagoons of fresh water 
and wooded with palms, reeds and other subtropical vegetation, 
remained as dry land from that time to the present. At the 
same time the low borders of the continent began to rise above 
the sea, forming a coastal plain of marshes and lagoons inhabited 
by tortoises, birds and other shore animals. It is well known that 
birds, seals and similar animals select for their rookenes, when 
possible, such islets as those described. Such locations give them 
security from predaceous animals, and an undisturbed breeding 
place for their young. 

As phosphoric acid has a greater affinity for lime than carbonic 
acid the carbonate of lime in such localities became converted 
into' the less soluble phosphate of lime, and as the process was 
continued for thousands of years, in all probability, the first steps 
in the formation of the invaluable phosphate beds of Florida were 
taken in this way. 

34 Character and Origin of the Tennessee Phosphates.-Sorne 
of the most extensive and valuable deposits of phosphates in the 
United States occur in Tennessee. The existence of these deposits 
■n commercial quantities was first pointed out in 1893 and since 
that time elaborate examinations of the extent and character 01 
the deposits have been made by the U. S. Geological Survey. 
35. Classification.-The phosphates of Tennessee are divided 

■» Hayes, The Tennessee Phosphates, 17th Annual Report of the Geolog- 

'"' s:?:'; Te'rstrwhuVr^^^^^^ 

iral Survey 1809-1900, Part III : 478- 

Ceolo'i: cal Atlas of the U.S., Columbia Koho, Tennessee. 

Sovev The Production of Phosphate Rock in ,903, Geological Survey. 

Mineral Resources of the United States, 1903 : 1047. 



OCCURRENCE OF BLACK PHOSPHATE 



33 



into two principal classes each of which has a number ot vane les. 
The two main groups are designated by their color, the blacK 
phosphate, which represents the original deposition and the white 
uhosphate, which is a secondary deposition or replacement. 1 he 
first group belongs to the Devonian age, and its members have 
been changed from their original form only by the process of con- 
solidation which affects all deeply buried sediments ; that is, they 
have been changed from a condition of mud and sand into com- 
pact rock exactly in the same manner as the non-phosphat.c bodies 
above and below them. The white phosphates, on the other hand 
probably do not occupy the position and form they had when first 
deposited. The material composing them has been translated 
from its original position and redeposited in an entirely different 

°The white phosphates are of comparatively recent origin, prob- 
ably having been formed in the last geological period preceding 

^le^'ocTurrence of Black Phosphate.-The black phosphates oc- 
cur first ir a nodular condition associated with green sandy shale. 
The nodules vary in size and shape from nearly spherical bodies 
from one-half to one and a half inches in diameter to irregular 
flattened ellipsoids, sometimes two feet in length and one-third or 
one-quarter as thick. Their surfaces are smooth and show no 
external evidence of organic origin. In weathering they produce 
almost a white powder, with fine and concentric banding of dif- 
ferent shades of gray. Thin sections examined unde the micro 
scope appear to be chiefly amorphous, with grains of pyrite and 
organic matter. In some of the nodules there is a concentric 
arrangement of the material, which is easily separated. The 
nodules in the lower layers are the largest. The number o£ 
nodules varies largely within short distances The nodtdes con- 
tain from 60 to 70 per cent, of tricalcitim phospha e. There 
a somewhat larger percentage of this substance in the weathec 
than in the unweathered rock. The nodules are easily separated 
from the materials in which they are imbedde.l, so that even when 
they are not sufficiently numerous to form almost continuous 
layers they can be mined with profit. 



Ill 



'»» 



^Ml 



34 



AGRICUI.TURAI. ANAI^YSIS 



The black phosphate also occurs in a bedded form and presents 
several varieties. Among these may be mentioned oolitic phos- 
phate, which has the appearance of a rusty, porous sandstone. 
The general appearance of the ovules of which the mass is made 
indicates that they were formed while -lying free upon the sea 
bottom. In the phosphatic limestone which at some points under- 
lies the phosphate bed, the same ovules and rounded fossil casts 
are seen scattered through the mass of calcite. Another variety 
of this bedded stone is known as compact phosphate, resembling 
a homogeneous, finely grained sandstone. The phosphatic grains 
of this rock are so small that they are distinguished with diffi- 
culty even with a magnifying glass. The composition of the rock, 
however, is revealed in a thin section under the microscope, and 
it is shown to be made up of small ovules and fossiled casts closely 
packed together. The ovules are nearly all flattened and are ar- 
ranged with their long axes parallel. 

Another variety is the conglomerate phosphate, which is closely 
associated with the oolitic and compact varieties, often entirely 
replacing them and consisting of beds of coarse sandstone or con- 
glomerate containing various amounts of phosphate. These con- 
glomerates are usually black or gray and the constituent grains 
are embedded in a matrix of fine material. They vary in size 
from extremely fine grains to coarse particles one-fourth of an 
inch in diameter. They are partly phosphate ovules, similar to 
those composing the oolitic rock, and partly quartz. The con- 
glomerate also contains many weather worn pebbles which are an , 
inch or more in diameter and composed of hard, black phosphate' 
so fine grained and homogeneous as to resemble black flint. 

There is also another variety known as shaly phosphate, in 
which the laminated structure is pronounced, the rock splitting 
into extremely thin sheetS. In other instances the layers are an 
inch or several inches in thickness, having a black glazed surface 
even more carbonaceous than the remainder of the rock. 

37. Occurrence of White Phosphates.— The white phosphates ap- 
parently present two types ; namely, the breccia and the bedded 
phosphate. Closer examination shows that the two varieties are 
more nearly related than was at first supposed, and they are found 



I- '■> 






I 



■5? 



->* 



I^AMEUvAR PHOSPHATE 



35 



grading into each other imperceptibly, so that the distinctions which 
were supposed to exist tend to disappear on more careful exam- 
ination. The result of this gradual merging has led to the drop- 
ping of the original classification and the bringing of the white 
phosphate into one group with a few slightly different varieties. 
Whatever may have been the original form of this rock, the 
j.hosphatic deposit is evidently secondary and is intimately asso- 
ciated with the rocks of the carboniferous period. The sections 
of this variety of phosphatic rock exhibit under the microscope 
masses of silica in which are bedded rhombohedral crystals, some- 
times very small and widely scattered, but perfect and sharply 
defined. In the granular portions of the rock the crystals are 
larger, appearing as sections of rhombohedrons which are not 
perfectly independent, but are segregated into irregular groups. 
These crystals, which have the form of calcite, have been en- 
tirely changed in their structure by the secondary deposit. Phos- 
phate of lime, in other words, has practically taken the place of 
the carbonate of lime in these crystals. The following analyses, 
made under the direction of Monroe, show the composition of this 
form of Tennessee white phosphate :^^ 

ANAI.YSES OF Tennessee White Stony Phosphate. 

I a 3 4 5 ■ 6 

Silica, SiO., 61.34 49-43 54-30 54.8S 50.18 56.46 

Lime, CaO 20.30 26.40 22.87 22.76 25.57 22.01 

Phosphoric acid, P0O5 12.55 15.12 14.86 15.30 15.21 13.15 

Corresponding to: 

Lime phosphate, Ca3 PaOg, and . . 27.40 33.00 32.45 33.40 33.20 28.60 

Lime carbonate, CaCOa 9-75 1521 9.36 8.23 13.45 ii-56 

38. Breccia Phosphate.— The breccia is the most abundant 
variety of the white phosphate. It occurs in irregular masses com- 
posed of slightly angular fragments of carboniferous chert im- 
bedded in a matrix of phosphate of lime. The phosphatic matrix 
before exposure to the weather is of a white or slightly reddish 
color and somewhat harder than compact chalk. 

39. Lamellar Phosphate.— Another variety of the phosphate is 
the white lamellar, consisting of even, parallel layers or plates. It 

^ 17th Annual Report of the U. S. Geological Survey, Part II, 1895-6 : 
539- 






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36 



AGRICULTUKAL ANAI^YSIS 



has evidently been formed by deposition of solutions, successive 
layers being slightly different in color and texture. In numerous 
cases the deposition seems to have taken place in a rather smooth 
cavity which was but partly filled with the deposited solution, so 
that deposition took place only on the bottom. 

40. Origin of the White Phosphates.— According to Hayes, the 
white phosphates of Tennessee originated as follows i^^ 
^ From the nature of the deposits of white phosphate, their rela- 
tions to other formations of the region, and the physical charac- 
teristics of the several varieties of the rock, there can be little 
doubt as to their mode of deposition. It seems reasonably certain 
that the rock is entirely a secondary deposit, accumulated subse- 
quently to the deposition of the carboniferous, Devonian and Silu- 
rian formations, with which it is now associated. The latter were 
laid down on the sea bottom as horizontal beds of sand, mud and 
shells, having great lateral extent. They were buried beneath 
other beds of sediment many hundred feet in thickness, which 
have since been removed by erosion. The black phosphate, as 
has already been explained, is one such sedimentary bed which 
was deposited when the conditions were favorable for'the accumu- 
lation of lime phosphate on the sea bottom. It was afterwards 
deeply buried by later deposited sediments, and has been brought 
to light by elevation of the sea bottom and erosion of the over- 
lying strata. 

Entirely different is the formation of the white phosphate. 
The lime phosphate of which these deposits are composed was 
doubtless originally extracted from sea water by organisms and 
accumulated together with other sediments, either segregated in 
beds and concretions or disseminated through limestones and 
shales. When these rocks were brought near the surface by up- 
lift and erosion they were attacked by percolating surface waters, 
which contain carbonic and other organic acids. These acids 
readily dissolve carbonate of lime, and to some extent also phos- 

'' The Tennessee Phosphates, by C. W. Hayes. Abstract from the 17th 
Annual Report of the Geological Survey, 1895-6, Part II, Economic Geology 
and Hydrography : 356. Also, Extract from the 21st Annual Report of 'he 
Geological Survey, 1899-1900, by C. W. Hayes, Part III, General Geoloev 
Ore and Phosi)hate Deposits : 479. 



I J 



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ORIGIN OF the: white PHOSPHATES 



37 



phate of lime. When water which has slowly percolated through 
the rocks at some depth emerges at the surface or into a cavity 
in which it is no longer subjected to pressure, the excess of car- 
bonic acid escapes, and the substances which had been held in 
solution by means of that acid may be redeposited. Thus many 
springs are now forming about their exits extensive deposits of 
materials which they have dissolved in the course of their under- 
ground passage. The most common spring deposits are calcare- 
ous, although siliceous and aluminous deposits are not uncom- 
mon, particularly in the case of thermal waters. When several sub- 
stances are held in the same solution the least soluble will gen- 
erally be the first to separate, and hence will form deposits nearer 
the exits. Also, when a solution of a difficultly soluble substance, 
as lime phosphate, comes in contact with one which is more easily 
soluble, as lime carbonate, there is generally an exchange effected 
— the more soluble substance is taken up and the less soluble one 
is deposited in its place. 

A simple application of these principles suggests the probable 
mode of formation of these deposits. The altitude at which they 
are found indicates that they were formed when the valleys of the 
region had about two-thirds of their present depth. The region was 
probably heavily forested, the decay of vegetation furnishing an 
abundant supply of organic acids to the percolating surface 
waters. It was also a region of sluggish streams, the valleys of 
which may have been to some extent occupied by swamps. The 
waters, thus highly charged with organic acids, descending 
through the more or less porous formations which occupy the 
higher portions of the country, dissolved calcium carbonate, and, 
in less quantity, calcium phosphate. The former, by reason of its 
greater solubility, was carried into the streams and thence to the 
sea. The phosphate, however, was deposited, the form of the 
deposits being modified by local conditions. In some cases the 
waters containing these substances in solution found an outlet in 
a mass of fragmental chert derived from the decay of the over- 
lying formations. Under such conditions the breccia was formed, 
the phosphate merely cementing the fragmental material. In 
other cases the waters flowed through open cavities of consid- 



'- if': 









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38 



AGRICUT^TURAI. ANALYSIS 



UTILIZATION OF THE WHITE PHOSPHATE 



39 



erable size. When these were the interstices among blocks of 
chert, there resulted the coarse breccia. The cavities were 
wholly or in part filled with compact phosphate, which shows, by 
differences of texture and color, that it was deposited from solu- 
tion in successive layers. In some cases it appears that the cavities 
were in a pure limestone. After they had been to a greater or 
less extent filled by the phosphate, by reason of some change in 
conditions, the limestone was dissolved, leaving the phosphate dis- 
seminated through the residual clay, which represents the original 
insoluble constituents of the limestone. Finally, in some places, 
instead of finding open cavities in w^hich the phosphate might be 
deposited, the solution, before emerging at the surface, came in 
contact with a siliceous limestone under conditions such that a 
transfer of materials was effected. The more soluble carbonate 
was taken up and the less soluble phosphate was deposited in its 
place. These conditions gave rise to the stony variety, in which 
the phosphate is clearly seen occupying the place originally held 
bv the carbonate. 

If this explanation of the origin of these phosphates is the cor- 
rect one, some important economic conclusions follow as to the 
extent of the deposits. So long as the waters were percolating 
slowly and at considerable depths they would take up rather than 
deposit phosphate. They would find conditions favorable for the 
latter process only comparatively near the surface, where the 
excess of carbonic acid might readily escape. Hence the deposits 
must not be expected to extend to any considerable depth. They 
are essentially superficial pocket deposits, and in most cases their 
depth will be limited by the depth of the residual mantle of chert 
and clay with which they are so intimately associated. It seems 
probable that the stony variety may extend to greater depths than 
any of the others, since the process to which it is attributed is 
one which does not depend directly on surface conditions — the 
escape of carbonic acid and the evaporation of the solution — but 
upon some conditions, not fully understood, favoring replace- 
ment. 

The deposits were probably much more extensive than now. 
The deepening of the valleys has removed the greater portion of 



.1 

J 



•J 



the original deposits, and those which remain are merely the rem- 
nants which have accidentally escaped erosion. 

41. Utilization of the White Phosphate.— From the foregoing 
description of the several varieties of white phosphate it will be 
readily understood that this rock is not available for shipment 
without undergoing some process of concentration. That a high- 
grade product can be obtained by the proper concentration is 
shown from the numerous analyses of selected hand specimens, 
which sometimes show as much as 80 per cent, of lime phosphate. 
Evidently the method of treatment should differ with the different 
varieties. The analyses already given show that the stony variety 
contains less than 50 per cent, of lime phosphate, and in it the 
phosphate is so intimately associated with the silica that no ready 
means of separating the two elements suggest themselves. In case 
of the other two varieties, however, the problem of concentration 
is a much simpler one. In case of the breccia, the properties which 
may be taken advantage of in separating the chert and the phos- 
phate are, first, differences in specific gravity, and, second, differ- 
ences in hardness. It has been suggested that the two constit- 
uents of the rock may be cheaply separated by some form of jig- 
ging apparatus. Determinations of their specific gravity, how- 
ever, do not offer much encouragement for this view. The chert 
is found to have a specific gravity varying from 2.61 to 2.69. 
The matrix of lime phosphate with which it is associated has a 
gravity of 2.83 to 3.07. This difference of 0.3 or 0.4 is probably 
not sufificient for any simple and cheap device. The specific 
gravity of the lamellar variety is somewhat higher than that of 
the structureless breccia matrix. 

The difference in hardness between the chert and the matrix 
suggests the possibility of making a high-grade concentrate, 
though not of making a complete separation of the two constit- 
uents of the rock. As already stated, when long exposed to the 
atmosphere the matrix becomes considerably indurated, so that it 
is separated from the chert with great difficulty. Below the sur- 
face, however, it seems probable that the phosphate will generally 
be found soft and granular, so that it can be easily pulverized 
and separated from the chert. The chert, on the other hand, shows 



mumjumMi%jiiiuiiu.M<t»mmummtm » 



40 



AGRICUI.TURAI, ANALYSIS 



little if any change of hardness from tliat at the surface If this 
softer breccia, therefore, were passed through a suitable crusher 
most of the phosphate would be pulverized, while the chert would 
remain in much larger blocks. If the material thus treated were 
passed over a screen with a proper mesh, which could be deter- 
mined only by experiments, it seems altogether probable that a 
fairly complete separation would be effected. The process sug- 
gested above would be a simple and cheap one, and, considering 
the ease with which the rock can be raised, it seems probable that 

a cheap and merchantable product could be obtained in this man- 
ner. 

A part of the lamellar variety would require no further treat- 
ment than hand picking at the bank. The quantity of such rock 
however, is probably not large, and the greater part of this variety' 

dilj'r. '^^r'"'*'^ ^'■°'" *' '^'y *'^™"8h which it is found 
disseminated. This would probably necessitate, first, screening in 
the bank, to separate it from the greater part of the clay ; second 
washing, to remove the remainder of the clay: and, third, hand- 
picking to remove the free chert with which it is associated. 

17lr! 7- '"■°''''" ''^ '^P'"^'^^' ^"^ >^ ^^^'■^f"! prospecting 
shall how tnis variety to exist in considerable quantities, it can 
doubtless be prepared for market at slight expense. It is im- 

Z^l u"' ^"" *'•' '"'''"^"' development of these deposits 
hat thorough prospecting should precede the erection of a plant 
for treating the rock. The prospecting should be done in a sys- 
tematic manner and by a competent engineer. 

STATISTICS AND COMPOSITION 
42. Tennessee Phosphates.-Tcnnessee produced during the 
year 1903, 460,530 pounds of phosphate rock containing from 
.7 to 80 per cent, of lime phosphate. It is well knovfn tha" 
almos all of the rich phosphates produced in Florida are ex- 
ported to Europe." Of the rich phosphates produced in T n- 
nessee however, only about one-fourth are sent to Europe. The 
other hree-fourths are consumed in this country. The Tennessee 
phosphates are not looked upon with very great favor in Europe 
hecause o their content of iron and alumina. Five samples of 

Annales de Chimie analytique, 1906, 1 1 : 256. • 



'k 

i 









PHOSPHATES FROM SOUTH CAROLINA DEPOSITS 4I 

Tennessee phosphate were found to have the following com- 
position : 

12345 

Insoluble (silica, etc.) 1.31 2.56 T.85 2.16 5.87 

Phosphoric acid 36.55 36.55 35.47 35.50 32.85 

Phosphate of lime 79.80 79.80 77.45 77.50 71.73 

Oxid of iron and alumina 2.00 2.48 3.16 3.88 4.52 

Carbonate of lime 13.27 12.05 ii-46 14.29 9.93 

Organic matters and water 3.62 3.11 6.08 3.17 7.95 

The above samples belong to what is known as the Brown Rock 
and come chiefly from the vicinity of Mt. Pleasant in Maury 
County. 

43. Blue Phosphate. — In Hickman County, which is adjacent to 
Maury County, large quantities of phosphate rock are found of 
a bluish gray tint and less rich in phosphate of lime than the de- 
posits above mentioned. These rocks are found to contain from 
60 to 70 per cent, of phosphate of lime, and from 2.5 to 5 per 
cent, of oxids of iron and alumina and from 1.5 to 5 per cent, of 
silica. The iron exists in these rocks partly in the form of pyrite. 
In Perry County another variety of phosphate of a reddish or 
white color is found with a still lower content of phosphate of 
hme, ranging from 30 to 50 per cent. These samples come from 
the surface. The interior deposits, on the contrary, are quite 
rich, containing from 70 to 75 per cent, of phosphate of lime- 
Still other deposits are found in Tennessee containing from yy 
to 80 per cent, of phosphate of lime and from two to three per 
cent, of oxids of iron and alumina. 

44. Phosphates from South Carolina Deposits. — It has been 
estimated that up to the present time there have been fur- 
nished to the markets from the South Carolina deposits about 
11,000,000 tons of rock, of which about one-third has gone to 
Europe. The discovery of the Florida phosphates was a severe 
blow to the industry in South Carolina, the annual exports from 
South Carolina having fallen to about 30,000 tons. The reason 
of this is that the South Carolina rocks are somewhat low in 
their content of phosphate of lime, ranging between 55 and 60 
per cent. Tliey contain from seven to 11 per cent, of carbonate 



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42 



AGRICULTURAL ANALYSIS 



of lime, from eight to 12 per cent, of silica, and from two to 
four per cent, of oxids of iron and alumina. 

Small deposits of phosphates occur in other parts of the United 
States ; namely, in North Carolina, in Pennsylvania, in Arkansas, 
and in Alabama. Lately deposits have also been found in Wyo- 
ming, in the county of Uinta, near the village of Cokeville, which 
are made up of grayish black phosphates in the form of heavy 
and very durable rocks. These deposits are found in the upper 
carboniferous rocks of the central Cordilleran region in a series 
of oolitic beds. 

Considerable quantities of phosphates are also produced in 
Canada. The smallness of the deposits and the difficulties of 
quarrying, however, have kept the Canada production down to a 
small amount, the production not exceeding 30,000 tons per year. 
It is estimated that only about 850,000 tons of phosphate rock are 
exported to Europe from the United States, principally from 
Florida and Tennessee, Florida leading with about 85 per cent, 
of the total exportations. 

45. Magnitude of Product. — In 1904 the production of phos- 
phates in the United States, principally in Florida, Tennessee 
and South Carolina, amounted to approximately 1,782,503 long 
tons, valued at $5703^582. This is an increase compared to 
1903 of 212,275 tons in quantity, and $709,670 in value. 
Exports in 1904, chiefly to Germany, France, Italy and 
Great Britain, totaled about 880,000 tons as against 785,259 
tons in 1903, showing an increase of 94,741 tons, or 12 
per cent. The ocean freight was $2.64 to $3.72, equivalent to 
from one-third to one-half of the c. i. f. prices paid for the phos- 
phates, which were $9.84 to $12.09 ^oi* Florida high-grade rock; 
$6.39 to $8.40 for land pebble ; $9.54 to $1 1.40 for Tennessee rock ; 
$5.61 to $6.88 for South Carolina rock. In competition with the 
American phosphates were exports of 775,000 tons from Africa, 
paying an ocean freight of $1.44 to $2.22, and selling in Europe 
at $6 to $7.60 for Algerian, and $5.75 to $6.60 for Tunis rock. 
There were also sent to Europe in 1904 some 125,000 tons high- 
grade phosphate from the Christmas and Ocean islands, paying a 
freight of about $6.48, and marketed at $11.75 to $14.45 P^i* ton, 



■I 



-i 



if 



4 









,^ 



PRODUCTION IN THE UNITED STATES 



43 



delivered. Summed up, Europe imported from the countries 
named a total of 1,780,000 tons valued at approximately $10,375,- 
683, of which $5,105,650, or over 50 per cent., represented cost of 
freight. 

The domestic trade, which takes little over half the production, 
showed some improvement in 1904, and prices ranged from $6.50 
to $7.50 per ton for high-grade rock, f. o. b. Florida ports ; $3.75 
to $4 for Florida land pebble ; $4 to $4.25 for Tennessee export 
rock, f. o. b. Mount Pleasant, and $2.95 to $4 for the various 
domestic grades; $2.75 to $3.50 for South Carolina rock, f. o. b. 
Ashley River. 

The industry in Florida is gradually coming under control of a 
few large miners, and the affiliation of important concerns has 
greatly lessened competition in the export trade. It is proposed 
to erect superphosphate plants, to utilize the large stocks of 70 
to yy per cent, rock in Florida. In Tennessee new capital has 
been invested in mining, and in South Carolina, because of the 
decadence of the river industry, work will be begun on the 
marsh lands on Morgan, Coosaw and Buzzard islands. 

Undoubtedly the most gratifying feature of the phosphate in- 
dustry to-day is the gradual elimination of speculative buying, and 
the introduction of economic management, which promises better 
profits for the future. 

46. Later Statistics. — The latest tabulated statistics relating 
to the phosphate industry in the United States are those found 
in the reports of the Geological Survey. The following tables 
taken from those documents show the rate of growth and the 
magnitude of the industry. 

47. Production in the United States. — The following table gives 
the production of phosphate rock in the United States in 1905 
and 1906, inclusive, based on the marketed product, classified by 
kinds or grades :^^ 



" Geological Survey, Mineral Resources of the United States, 1906 : 



1080. 



■1: 



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44 



AGRICUI.TURAL ANALYSIS 



Production of Phosphate; Rock in the United States, 1905-1906, 

Based on the Quantity Marketed. 



1905 

< 



Quantity 
(long tons) 



State 
Florida : 

Hard rock . . 
Land pebble 
River pebble 
Total. . . 
South Carolina 
Land rock • - 
River rock. . . 
Total .... 
Tennessee : 
Brown rock. . 
Blue rock . . . 
White rock . . 

Total 482,859 

Other States^ 

Grand total. 1,947,190 



Value 



Aver- 
age 

value 
per 
ton 



1906 



Quantity 
(long tons) 



Value 



Aver- 
age 

value 
per 
ton 



577,672 12,993,732 $5.18 587,598 ^,440,276 fo.85 



528,587 

87,847 
1,194,106 

234,676 

35,549 
270,225 

438,139 
44,031 

689 



^ Includes Arkansas and Idaho 



1,045,113 ^-98 

213,000 2.42 

4,251,845 3.56 

774,447 3-30 

103,722 2.92 

878,169 3.25 

1,509,748 3.45 

121,486 2.76 

2,155 3-^3 

1,633,389 3.38 

• ••••••• •••• 

6,763,403 3-47 



675,444 
41,463 
1,304.505 

190,180 

33,495 
223,675 

510,705 
35,669 

1,303 

547,677 

5,100 

2,080,957 



2,029,202 

116,100 

5,585,578 

711,447 
105,621 

817,068 

2,027,917 
114,997 

5,077 

2,147,991 
28,800 

8,579,437 



3.00 
2.80 
4.28 

3-74 
3.15 
3-65 

3-97 
3.22 

3.90 

3-92 

5-65 
4.12 



48. Marketed Production.— Since 1880 the quantity and the 
value of the phosphate rock produced (marketed) In the United 
States have been as follows : 

Marketed Production (I,ong Tons) of Phosphate Rock in the 

United States, 1880-1906. 



Year 

1880.. 

1881.. 

1882.. 

1883.. 

1884.. 

I 005 • • 

1886... 

1887... 

1888.. . 

1889... 

I 890 . . . 

1891 . . . 

1892. . . 

1893... 



Quantity 

211,377 
266,734 

332,077 

378,380 

431,779 

437,856 

430,549 
480,558 

448,567 
550,245 
510,499 
587,988 

681,571 
941,368 



Value 

11,123,823 

1,980,259 

1,992,462 

2,270,280 

2.374,784 
2,846,064 

1,872,936 

1,836,818 

2,018,552 

2,937,776 

3,213.795 
3,651,150 
3,296,227 
4,136,070 



Year 
1 894 . . . 
1895. . . 
1896. . . 
1897. . . 
1898... 
1 899 . . . 
1900. . . 
1 901 . . . 
1902. . . 
1903... 
1904 • . 
1905... 
1 906 . . . 



Quantity 
996,949 
1,038,551 

930,779 
1,039,345 
1,308,885 

1.515,702 
1,491,216 

1,483,723 
1,490,314 
1,581,576 
1,874,428 

1,947,190 

2,080,957 



Value 

fo,479.547 
3,006,094 

2,803,372 

2,673,202 

3,453.460 

5,084,076 

5,359.248 
5,316,403 

4,693,444 

5,319.294 
6.580,875 

6,763,403 
8,579,437 



49. Imports.— The following table shows the imports of fer- 



'4 



'- M 



CKNERAL OBSERVATIONS 



45 



tilizers of all kinds into the United States for the years 1903- 
1906, inclusive: 

Fertii^izers Imported and Entered for Consumption in the 
United States, 1903-1906, in Long Tons. 



Guano 



Kieserit and 
Kainit 



Apatite, bone dust, crude 
phosphates, and other 
substances used only 
for manure 



Total 
vahie 



Year Quantity Value Quantity Value Quantity Value 

1903 21,985 1252,132 158,313 $ 773,758 246,042 $2,231,575 13,257,465 

1904 37,127 498,702 218,957 1,050,082 243,130 2,455,618 4,004,402 

1905 27,104 379,667 351.053 1,850,622 197,115 2,450,835 4,681,124 

1906 23,222 322,766 334,843 1,790,969 211,274 2,598,451 4,712,186 

50. World's Production. — In the following table will be found 
a statement of the world's production of phosphate rock from 
1903 to 1905, inclusive. 

WoRivD's Production of Phosphate Rock, 1903-1905, by 

Countries, in Metric Tons. 



1903 



1904 



1905 



Quantity Value 
320,843 fl, 238,454 



Quantity Value Quantity Value 

343,317 11,325,104 334,784 $1,225,126 



23,307 

193,305 

1,179 



332,292 
8,425 



99,519 (M 

476,720 2,093,118 

{') 

2,522 33,76s 



Country 

Algeria 

Aruba (Dutch 
West Indies) 15,749 

Belgium 184, 1 20 

Canada 1,251 

Christmas Is- 
land (Straits 
Settlements) 71,218 

France 475,783 

French Guiana 7,893 

Norway ^>795 

Redonda (Brit- 
ish West In- 
dies) 1,102 

Russia 14,635 

Spain 1,124 

Sweden 3>2i9 

Tunis 352,088 

United King- 
dom 71 

United States.. 1,606,881 

^ Value not reported. 

'^ Statistics not yet available. 

51. General Observations. — The foregoing data show, as stated 
in the report, that the out])nt of phosphate rock in the United 



332,250 
8,214 



2,115,647 
60,023 

24,120 



7,207 

47,580 

5,968 

8,627 

1,260,137 

423 



23,128 
202,480 

832 



72,905 
423,521 

n 
1,456 



1,729 

3,305 
2,929 

455,197 
59 



252,263 
4,590 



1,909,859 
19,564 



10,498 

19,136 

6,279 

1,582,165 

423 



1,370 

n 

521,731 1,812,493 



7,295 



5,319,294 1,904,418 6,580,875 1,978,345 6,763,403 



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: . : ■ 



rt'l 









m 



n 



lii 



Hi 



1 *> 



46 



AGRICULTURAI, ANAI^YSIS 



THE VALUE OF BONE MEAL 



States in 1906 was 2,080,957 long tons, valued at $8,579,437. 
A comparison of tlie figures of late years indicates that, although 
the output has usually increased each year, the demand has 
made even more rapid strides, and that the tendency of the 
market price is upwards. The new Western fields will probably 
help to supply the increasing demand, but as their market is 
somewhat local they will not materially affect the general con- 
ditions throughout the country. The demand will be likely to 
continue in excess of the supply unless the new Tennessee field 
proves to be more extensive than is anticipated. The outlook 
for the newer fields is therefore bright and will soon become 
even more promising as the older fields become exhausted. It 
is not impossible that the increasing demand and higher prices 
will make it possible to operate many low grade deposits which 
it has hitherto been impracticable to utilize. 

52. Quantity of Phosphoric Acid Removed by Crops.— It is esti- 
mated that the quantity of phosphoric acid removed froni the soil 
annually in the United States is equivalent to that contained in 
7,000,000 tons of 14 per cent, superphosphate.^* This estimate 
does not include the quantity removed by erosion and leaching. It 
is evident that in order to maintain the present fertility of our 
arable soil in respect of phosphoric acid about one million tons of 
this substance, calculated as Pfir,, must be added to the soil each 
year. 

53. General Conclusions. — From the study of the origin of the 
deposits of mineral phosphates it appears that those which are 
suitable for economic uses have been derived chiefly from the 
decay of organic matter— mostly of animal origin. The phos- 
phoric acid was evidently very generally diffused in the mineral 
matter which first formed the crust of the earth. It began to be 
utilized by the simplest forms of vegetable growth which first 
appeared on the earth's surface, and through this intermediary 
passed into animal organisms. In these it was finally segregated 
in the bones in large quantities. In the decay of animal bodies 
the bony structure is attacked by solvents; for instance, the nitric 
acid produced by the oxidation of the protein of vegetable and 

^* Voorhees, Journal of the Frauklin Institute, 1905, 160 : 211. 












47 



animal origin, by the carbonic acid in water and by the humic 
acids of the soil. The solutions thus produced are carried into 
the soil where a complex series of actions due to unstable chem- 
ical equilibria takes place. The phosphoric acid which in the 
bones is combined with lime as tricalcium phosphate, and which in 
solution is in the form of free acid or as monocalcium phosphate, 
tends again to form more stable compounds and is finally deposited 
chiefly in the form in which it existed in the bones, viz., trical- 
cium phosphate. All these changes take place strictly in harmony 
with the laws of physical chemistry. The deposits of phosphates, 
therefore, are due to chemical rather than geological phenomena. 

54. The Value of Bone Meal from which the Nitrogen Constit- 
uents Have Been Extracted, as a Fertilizing Reagent.— When 
fresh, finely ground bones are applied to use as a fertilizer and 
valuable results are obtained they may be ascribed either to the 
nitrogen constituent in bone or to its content of phosphoric acid. 
In general, the bone phosphate has not been regarded as being 
of great value, and the chief utility of ground bone has been 
ascribed to its nitrogen constituent. If the value of a phosphate 
as a fertilizer be governed by its solubility in ammonium citrate 
or citric acid, it has been shown that considerable portions of 
phosphoric acid in finely ground bone are soluble in these re- 
agents. 

Since the original observations of Huston have shown that the 
phosphoric acid of finely ground bone is soluble in ammonium 
citrate, this problem has been studied by many other observers. 
Reitmair has made investigations on this subject with the results 
which follow. ^^ The observations were carried on at the same 
time with degelatinized bone meal and basic slags, and the quan- 
tity of rye produced per hectare when these bodies were used 
for the fertilizing reagents was determined. As a result 
of these investigations Reitmair concluded that the solu- 
biHty of a phosphate in citric acid is no criterion for its value as 
a fertilizer or as a measure of its solubility in the soil. The solu- 
bility in citric acid of phosphate is no measure for the quantities 
of the active forms of phosphoric acid which are given. It is 

'^ Wiener landvvirtschaftliche Zeitung, 1905, 55 : 879-8S1 and 889-891. 



-1^1 






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(ill 

i 



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.-I 



i 

i H 



iH 






48 



AGRICUI.TURAL ANALYSIS 



CONSTITUENTS TO BE DETERMINED 



not even a measure, as has often been supposed, of the favorable 
mechanic properties of phosphatic manure. The larger particles 
of bone phosphate and of basic slags were brought into solution 
both by the usual and by the modified digestion methods prac- 
ticed. Various samples of the bone meal from different sources 
were treated with citric acid, according to the usual method to 
oeterm.ne the percentage of solubility therein, and the quantity 
ot fine particles, passed through a sieve with fine mesh, was de- 
termined. A bone meal containing 86.5 per cent, of fine particles 
showed a solubility of 92.3 per cent, in citric acid, while the de- 
gelatinized sample of bone meal containing onlv 12 6 per cent of 
fine particles showed a solubility of 87.6 per cent. Thus while 
It IS generally true that the solubility in citric acid varies inversely 
with the size of the particles, it does not vary proportionately 
thereto. The period of digestion in each case was one-half hour 
It IS evident from the above that the agricultural chemist has 
yet much to learn concerning the character and speed of the solu- 
tion of phosphate in a soil. The changes which take place in the 
ordinary digestion in citric acid in the laboratory are evidently 
of a very different degree of magnitude and are carried on with 
a very different degree of speed from that which takes place dur- 
ing the growing period in the soil itself. 

All the experiments conducted by Reitmair indicate that the 
degelatinized phosphoric acid has a distinct value as a phosphatic 
fertilizer and this depends primarily upon the state of subdivision 
and IS indicated only appro.ximately by its solubilitv in citric acid 
Attention, however, must be called to the fact that in the manu- 
facture of degelatinized bone meal it has not yet been possible to 
produce a product entirely free from nitrogen on a commercial 
scale. The last traces of nitrogen are not removed and 
there usually remains in the degelatinized bone about 
0.5 per cent, of nitrogen. This residue must be re- 
garded as an unavoidable contamination of the bone 
meal for experimental purposes, but it is of a magnitude so 
small as to be practically ignored in the experimental work It is 
evident, therefore, that any attempt to determine the fertilizing 
value either of degelatinized bone or of basic slag by its solubility 



49 



in citric acid solutions is likely to lead to erroneous conclusions. 
Moreover, the fertilizing value of any material of this kind is 
not a constant quantity, but varies always with the character of 
the soil to which it is applied and of the seasonal environment to 
which it is subjected. The chemist has done all that could be 
reasonably expected of him when he has determined the fineness 
of the subdivisions of the material and its relative solubility in 
certain reagents which indicate the relative amount of acid pres- 
ent which readily passes into solution under the ordinary condi- 
tions to which it is likely to be subjected. It must be remem- 
bered, however, that in the field the processes of solution go on 
constantly for a period of three or four months; in fact, as 
long as the plant continues feeding. A very feeble solubility in 
the soil, therefore, would render the phosphoric acid constantly 
available in the proportion in which it is used. If a reagent of 
the same feeble power was used in the laboratory it would neces- 
sarily have to be kept in activity over a long period of time to 
yield results which are comparable to those found in the soil. 
Therefore, it seems only reasonable to use a stronger reagent 
for a limited period of time such as can be used practicably by 
the analyst for his determinations. 

While the use of the various reagents which have been pro- 
posed for the valuation of these materials may not lead to results 
directly comparable to those that take place in the growing sea- 
son, they do, undoubtedly, give an idea of the availability, which 
13 of great practical importance. 

ANALYTICAL PROCESSES 

55. Constituents to be Determined.— The most important point 
111 the analysis of mineral phosphates is to determine their con- 
tent of phosphoric acid. Of equal scientific interest, however, 
and often of great commercial importance is the determination 
of the percentage of other acids and bases present. The analyst 
is often called on, in the examination of these bodies, to make 
known the content of water both free and combined, of organic 
and volatile matter, of carbon dioxid, sulfur, chlorin, fluorin 
sihca, iron, alumina, calcium, manganese, magnesia, and the al- 
kalies. The estimation of some of these bodies presents problems 



i ■-; I 



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; ■t '! I 



H 
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50 



AGRICUI.TURAI, ANAI^YSIS 



CONDUCT OF THE INCINERATION 



51 



of considerable difficulty, and it would be vain to suppose that the 
best possible methods are now known. Especially is this the case 
with the processes which relate to the estimation of the fluorin, 
silica, iron, alumina, and lime. The phosphoric acid, however, 
which is the chief constituent from a commercial point of view, 
it is believed, can now be determined with a high degree of pre- 
cision. Often the estimation of some of the less important con- 
stituents is of great interest in determining the origin of the de- 
posits, especially in the case of fluorin. While the merchant is 
content with knowing the percentage of phosphoric acid and the 
manufacturer asks in addition only some knowledge of the quan- 
tity of iron, alumina, and lime, the analyst in most cases is only 
content with a complete knowledge of the constitution of the 
sample at his disposal. 

56. Dissolving the Phosphoric Acid. — It often happens, in the 
case of a mineral phosphate, that the only determination desired 
is of the phosphoric acid. In such a case the analyst may pro- 
ceed as follows: If the qualitative test shows the usual amount 
of phosphoric acid, two grams of the sample passed through a 
sieve, with a millimeter, or, better, a half millimeter mesh, are 
placed in a beaker and thoroughly moistened with water. The 
addition of water is to secure an even action of the hydrochloric 
acid on the carbonates present. The beaker is covered with a 
watch-glass and a little hydrochloric acid is added from time to 
time until all effervescence has ceased. There are then added 
about 30 cubic centimeters of aqua regia and the mixture is raised 
to the boiling-point on a sand-bath or over a lamp. The heating 
is continued until chlorin is no longer given off and solution is 
complete. The volume of the solution is then made up to 200 
cubic centimeters without filtering, filtered, and an aliquot part 
of the filtrate, usually 50 cubic centimeters, representing half a 
gram of the original sample, used for the determination of the 
phosphoric acid according to some one of the accredited methods. 
The small quantity of insoluble material from phosphates of the 
usual composition does not introduce any appreciable error into 
the process when the volume is made up to 200 or 250 cubic 
centimeters. 



H 



i 



INCINERATION IN A MIXTURE OF SULFURIC AND 

NITRIC ACIDS 

57. Destruction of Organic Matter. — The preliminary destruc- 
tion of the organic matter for the purpose of determining the 
phosphoric acid and other mineral matters, save sulfur and nitro- 
gen, may be conveniently conducted as follows : 

Neumann has proposed incineration in a mixture of sulfuric 
and nitric acids as a convenient method of preventing the forma- 
tion of free carbon, which is destroyed very slowly by subsequent 
burning.2« The acid mixture is prepared by pouring slowly 
and with constant shaking, one-half liter of concentrated sul- 
furic acid into one-half liter of concentrated nitric acid of a 
specific gravity of 1.4. 

58. Apparatus. — The incineration is carried on in a deep, round 
flask of Jena glass which has the normal length of neck of about 
10 centimeters and a capacity of from one-half to three-fourths 
of a liter. Over this is placed in a glass or porcelain ring a funnel 
provided with a stop-cock, which is conveniently provided with 
a capillary dropping-tube, and the whole apparatus is fixed to an 
appropriate stand. In the preparation of the sample different 
processes are employed, according to the condition of the sam- 
ple. Dry, powdery substances are placed in small glass tubes 
(weighing tubes) wdiich can be easily passed into the neck of the 
incineration flask. Sticky substances can be placed in a piece of 
a broken test-tube. Liquids can be placed in thin, weighed, small 
tubes which are easily broken after placing in the flask. Dry or 
moist substances can be used for the incineration, and even liquids 
in not too large quantities, without any previous preparation. In 
the case of blood it is better to evaporate it before incineration. 
Fats or materials rich in carbohydrates, such as milk, should be 
treated before incineration with one per cent, of pure potash lye 
and evaporated to a sirupy consistence in order to avoid foaming 
or bumping in the flask. For instance, for 25 cubic centimeters 
of milk about 15 cubic centimeters of one per cent, potash lye 
are used. 

59. Conduct of the Incineration. — The substance which has been 

'* Zeitschrift fiir ])hysiologische Chemie, 1902-3, 37 : ii5- 



pi 



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1 1] 



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52 



AGRICULTURAL ANALYSIS 



LOSS OF PHOSPHORIC ACID BY INCINERATION 



53 



prepared in some of the ways described is placed in the flask and 
a measured quantity of the acid mixture, from five to 
10 cubic centimeters, poured over it and warmed with a 
moderate flame. As soon as the evolution of brown 
nitroso-vapors becomes slow a further addition of the 
acid mixture, drop by drop, from the funnel furnished with 
a stop-cock, is added and this addition continued until the re- 
action ceases and the intensity of the brown vapors evolved is 
diminished. In order to determine whether the destruction of 
the material has been completed, the addition of the acid mixture 
is discontinued for a short time and the mass further heated until 
the brown vapors formed disappear and it is noticed whether 
the liquid in the flask is still dark or black. If this is the case 
the acid mixture is again added and the test above 
described, after a few minutes, is repeated. If on standing 
and after the expulsion of the brown vapors the bright 
yellow or colorless liquid is not again darkened by further heat- 
ing, and also no evolution of gas is observed, the incineration may 
be regarded as complete. If the liquid is colored slightly yellow 
it generally becomes completely clear on cooling. Three times 
as much water is now added as the quantity of acid mixture 
which has been used, the mixture heated and boiled from five to 
10 minutes. By this process brown vapors are evolved which 
are derived from the decomposition of the nitrosyl sulfuric acid 
which has been formed. 

It must be remembered that in the above operation the nitro- 
gen of tlie protein matter is not converted into ammonia. In 
fact, no trace of ammonia can be found in the resulting liquid. 
The ash constituents, however, of the organic matter are found 
in a completely inorganic state dissolved in the mixture, and this 
mixture can be used for the determination of these constituents 
in the ordinary way. 

The above method for freeing the phosphorus and converting 
it into inorganic forms has given good results in the laboratory 
of the Bureau of Chemistry. 

60. Loss of Phosphoric Acid by Incineration.~It is well known 
that in certain substances used for fertilizing i)urposes, such as 



II 



oil cakes and other organic compounds, the large quantity of 
phosphoric acid which they contain is in organic combination 
and unless special precautions are exercised a portion of the 
phosphorus is lost in burning. The loss of phosphoric acid which 
takes place in cereals has lately been carefully studied by Leavitt 
and LeClerc.-^ In the case of wheat it is shown that the 
principal part of the organic phosphorus is in a water-soluble 
form, known as phytin. This substance has a relatively high 
molecular weight compared to the phosphorus molecule. A 
comparatively large percentage of the phosphorus may be lost 
in ashing without changing very greatly the apparent weight of 
the ash. 

As is well known, the addition of calcium acetate previous to 
burning prevents the volatilization of phosphoric acid. The pro- 
portion of phosphorus lost by the ordinary incineration as com- 
pared with the amount obtained with the previous addition of 
calcium acetate has been found in the extreme cases to be 50 per 
cent, of the total quantity present. The ordinary incineration 
was conducted at redness. If, however, the incineration is ac- 
complished without any treatment whatever at incipient redness 
just sufficient to show a faint radiation of light from the dishes, 
there is no appreciable loss of phosphoric acid. The results 
show that the ashing below the point of fusion of the mineral 
portions of the ash is not a very important factor where only the 
percentage of ash is desired. But in order to determine the 
. quantity of the phosphorus as phosphoric acid the greatest cau- 
tion must be observed to keep the temperature below the volatil- 
ization point of the combined phosphorus. This is to be ac- 
coniplished either by incineration at an extremely low tempera- 
ture or by previous treatment with calcium acetate. 

Later investigations show that in reality there is no appreciable 
loss of phosphoric acid even at bright redness. The phosphoric 
acid is simply changed into a form which is not precipitable by 
ammonium molybdate until the ash has been boiled a long time 
with nitric acid, or has been treated according to Neumann's 
method of digesting with nitric and sulfuric acid. 

" Journal of the American Chemical Society, 1908, 30 : 391, 617. 



54 



AGRICULTURAL ANALYSIS 



PRELIMINARY CONSIDERATIONS 



55 



6i. Official Method. — The official chemists recommend seven 
metkods of sohition for mineral phosphates, phosphatic materials 
and preparations thereof; viz.,^^ 

1. Ignite and dissolve in hydrochloric acid. 

2. Evaporate with five cubic centimeters of magnesium nitrate 
solution and dissolve in hydrochloric acid. This method is ap- 
plicable in the presence of organic matter. 

3. Boil with from 20 to 30 cubic centimeters of strong sulfuric 
acid, adding from two to four grams of sodium or potassium 
nitrate at the beginning of the digestion and a small quantity, 
after the solution has become nearly colorless. Or the nitrate in 
small quantities may be added at regular intervals during the 
whole time of the digestion, which is conducted in a kjeldahl 
llask marked at 250 cubic centimeters. When the solution is 
colorless add 150 cubic centimeters of water, boil for a few 
minutes, cool and make up to the mark with water. 

4. Digest with strong sulfuric acid and such other reagents as 
are used in the processes for converting nitrogen in nitrogenous 
compounds into sulfate of ammonia as described in the second part 
of this volume. Do not add any potassium permanganate but 
after the solution has become colorless add about 100 cubic centi- 
meters of water, boil for a few minutes, cool and make up to a 
convenient volume (250 cubic centimeters). The operation should 
be conducted on about 2.5 grams of substance. 

Processes 3 and 4 are especially applicable to organic sub- 
stances such as oil cakes, which contain considerable quantities 
of phosphorus. 

5. Dissolve in 30 cubic centimeters of concentrated nitric and a 
small quantity of hydrochloric acid and boil until organic matter 
is destroyed. 

6. Add to the substance 30 cubic centimeters of concentrated 
hydrochloric acid, heat and add cautiously in small quantities at 
a time about 0.5 gram of finely pulverized potassium chlorate to 
destroy organic matter. 

7. Dissolve the substance in from 15 to 30 cubic centimeters of 
strong hydrochloric acid and from three to 10 cubic centimeters 

^ Bureau of Chemistry, Bulletin 107, 1907 : 2. 



of nitric acid. This method is particularly suited to samples con- 
taining much iron or aluminum phosphate. 

From the above directions it is seen that in a purely mineral 
phosphate a single strong acid or a mixture of acids is sufficient 
to bring all the phosphoric acid into solution. Where orgamc 
matter is present the use of strongly oxidizing solvents as in 
4 and 5 is necessary. In substances containing phosphorus m 
organic forms such as blood, tankage, oil cakes, seeds, etc., espec- 
ial care is required to complete the oxidation and secure all the 
phosphorus in the form of phosphoric acid. 
GENERAL METHODS FOR ESTIMATING PHOSPHORIC 

ACID IN FERTILIZERS 
62 Preliminary Considerations.— The chief sources of the 
phosphoric acid in commercial fertilizers are the mineral phos- 
phates and bones. In respect of the general analyses of mmeral 
phosphates detailed directions have been given in the precedmg 
volume. Bones are valuable for fertilizing materials, both because 
of their content of phosphoric acid and of their organic nitrogen. 
The method of treating bones for their phosphoric acid will be 
found in the general methods for fertilizing materials, and their 
nitrogen content can be determined by the processes to be de- 
scribed hereafter. Other fertilizing materials also contain phos- 
phorus, as ashes, tankage, oil cakes, and other organic products. 
In general, the methods for determining the phosphoric acid is 
the same in all cases, but the means of destroying the organic 
matter precedent to the analysis vary in different cases. In most 
cases a simple ignition is sufficient, while, if the phosphorus be 
found in certain organic products, the oxidation must be accom- 
plished bv one of the methods described in the processes adopted 
by the official chemists. In all cases of acid phosphates 
and superphosphates, the water and ammonium citrate-soluble 
phosphoric acid is to be determined as well as the total. ^ In 
basic slags the amount soluble in ammonium citrate or dilute 
citric acid is also to be ascertained. 

In all cases where soluble or so-called reverted acid is to be 
considered, the analysis must be performed without previous 
desiccation or ignition. If water content or loss on ignition is 



II 



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56 



AGRICUI^TURAI, ANAI.YSIS 



PREPARATION OF REAGENTS 



57 



to be considered, the operation to determine them must be con- 
ducted on a separate part of the sample. 

The methods of analysis which have been adopted by associa- 
tions of chemists should be given the preference in the conduct of 
the work, although it must be admitted that they may contain 
sources of error, and may be in no respect superior to processes 
employed by chemists in their private capacity. In this country 
the methods adopted by the Association of Official Agricultural 
Chemists should be followed as closely as possible. The great 
merit of other methods, however, must not be denied. Espe- 
cially those methods which shorten the time required or diminish 
the labor and expense of the analysis are worthy of careful con- 
sideration. In factory work, for instance, it is often far more 
important for the chemist to be able to rapidly determine the 
phosphoric acid in a great number of samples with approximate 
accuracy than to confine his work to one with absolute precision. 
Some of the shorter methods, moreover, notably the citrate or ti- 
tration process, appear to be quite, if not altogether, as reliable 
as the molybdate method, while in the case of the uranium volu- 
metric process, it must not be forgotten that it has been largely 
practiced in France. Other volumetric processes are given 
in full, as, for instance, the one perfected by Pemberton and Kil- 
gore, and data are at hand to justify their strong recommendation 
It should be remembered that this manual is not written for the 
beginner, but rather for the chemist already acquainted with the 
principles and practice of general chemical analysis, and it is 
therefore, expected that each analyst will make intelligent use of 
the data placed at his disposal. 

63. Preparation of neRgents.—A7mnoniHm Citrate Solution.— 
(a) Mix 370 grams of commercial citric acid with 1500 cubic 
centimeters of water, nearly neutralize with commercial ammonia 
cool, add ammonia until exactly neutral (testing with saturated 
alcoholic solution of corallin) and bring to a volume of two liters 
Determme the specific gravity, which should be 1.09 at 20^ be- 
fore using. 

(b) Optional Metlwd.-To 370 grams of commercial citric 
acid add commercial ammonia, of 0.96 specific gravity, until near- 



ly neutral; reduce the specific gravity to nearly 1.09 and 
proceed as follows: Prepare a solution of fused calciuiri 
chlorid 200 grams to the liter, and add four volumes of 
strong alcohol. Make the mixture exactly neutral, using a 
small amount of freshly prepared corallin solution as a prelimi- 
nary indicator, withdrawing a portion, diluting with an equal 
volume of water, and testing with cochineal solution. Fifty cubic 
centimeters of this solution will precipitate the citric acid from 
10 cubic centimeters of the citrate solution. To 10 cubic centi- 
meters of the nearly neutral citrate solution add 50 cubic centi- 
meters of the alcoholic calcium chlorid solution, stir well, filter 
at once through a folded filter, dilute with an equal volume of 
water and test the reaction with neutral solution of cochineal. If 
acid or alkaline, add ammonia or citric acid, as the case may be, to 
the citrate solution, mix, and test again as before. Repeat this pro- 
cess until a neutral reaction of the citrate solution is obtained. 
The specific gravity must be T.09 at 20°. 

The reagents employed in the separation of the phosphoric 
acid are prepared according to the following formulas : 

Molybdate Solution.— Dissolve 100 grams of molybdic acid in. 
144 cubic centimeters of ammonia, specific gravity 0.90, and 271 
cubic centimeters of water ; pour the solution thus obtained, slow- 
ly and with constant stirring, into 489 cubic centimeters of nitric 
acid, specific gravity 1.42, and 1148 cubic centimeters of water. 
Keep the mixture in a warm place for several days, or until a 
portion heated to 40° deposits no yellow precipitate of ammo- 
nium phosphomolybdate. Decant the solution from any sedi- 
ment and preserve it in glass-stoppered vessels. 

Ammonium Nitrate Solution.— Dissolve 200 grams of com- 
mercial ammonium nitrate in water and dilute with water to two 

liters. 

Mamesia Mixture.— Dissolve 22 grams of recently ignited 
calcined magnesia in dilute hydrochloric acid, avoiding an ex- 
cess of the latter. Add a little calcined magnesia in excess, and 
boil a few minutes to precipitate iron, alumina, and phosphoric 
acid; filter; add 280 grams of ammonium chlorid, 700 cubic centi- 
meters of ammonia of specific gravity 0.96, and water enough to 



f- 



58 



AGRICULTURAL ANALYSIS 



make a volume of two liters. Instead of the solution of 22 grams 
of calcined magnesia, 1 10 grams of crystallized magnesium chlorid 
(MgCl^.eHjO) may be used. 

Dilute Ammonia for Washing. — This solution is prepared so 
as to contain 2.5 per cent. NH3. 

Magnesium Nitrate Solution. — Dissolve 320 grams of cal- 
cined magnesia in nitric acid, avoiding an excess of the latter; 
then add a little calcined magnesia in excess ; boil ; filter from th- 
excess of magnesia, ferric oxid, etc., and dilute with water to two 
liters. 

Formulas for the Reactions. — The reactions which take place 
when a mineral acid, for instance, nitric, dissolves tricalcium 
phosphate, may be represented as follows: Ca,(PO02+4HNO3 

=Ca(H2POj2+2Ca(NO,)2- In the case of a large excess of 
acid, free phosphoric acid may be formed thus: 

Ca3(POJ,+6HN03=3Ca(NO.,),+2H,PO,. 
Assuming that the phosphoric acid is in a soluble state in the 
solutions prepared with the strong hot acids, the reactions which 
tske place in the process of separating it are as follows : 

1. (For free phosphoric acid) : 

2H3PO,+24 ( NH J ,MoO,+42HN03=2 ( NH J ,P0,. 12M0O, 

+42NH,N03+24HjO. 

2. (For monocalcium phosphate) : 

Ca(H,PO,)2+24(NHJ,MoO,+44HN03=2(NHJ3PO,. 

i2Mo03+Ca(NH3),+42NH,N03+24H,0. 
The yellow precipitate 2(NHj3PO<.i2Mo03 is dissolved in 
ammonia with regeneration of ammonium molybdate as follows : 

3. 2(NHJ3PO,.i2Mo03+48NH,OH=2(NHJ.,PO,+ 

24 ( NH J 2MoO,+24H20. 

4. Precipitation of the phosphoric acid with magnesia salts: 

(NH,)3PO,+MgCl,=NH,MgPO,fNH,Cl. 

5. Conversion of the ammonia-magnesium phosphate into mag- 
nesium pyrophosphate by heat: 

2NH,MgPO,=Mg,P,0,-f2NH3+H,0. 
The factors for calculating the phosphorus pentoxid and tri- 



OFFICIAL METHOD FOR TOTAL PHOSPHORIC ACID 59 

calcium phosphate from the weight of pyrophosphate are given be- 
low on the two bases, viz., hydrogen equals i, and oxygen 

equals 16. 

H=i. 

MgjP^O, Xo.63756=P205 
Mg2P20,Xi.39i8=Ca3(PO,)j 

P.6,X2.i83i=Ca3(PO,)2 

0=16. 
Mg,P20,Xo.63757=P205 
Mg.,PAXi-3932=Ca.,(PO,)i. 

P,65X2.i852=:Ca3(P04)2 
64 Official Method for Total Phosphoric Acid.— Having now 
described the approved methods of bringing into solution all the 
phosphorus in the form of phosphoric acid, the next step is to 
separate this acid and bring it into a homogeneous compound in 
which it may be titrated or weighed. The usual method of 
separation depends on the property possessed by phosphoric acid 
of forming in a strongly acid solution, which prevents the pre- 
cipitation of the associated bodies, an insoluble compound with 
molybdic acid. The separation is accomplished as follows: 

Determination.— Ntntr^Wzt an aliquot portion of the solution 
prepared as above, corresponding to 0.25 gram, 0.50 gram, 
or one gram, with ammonia, and clear with a few drops of nitric 
acid In case hydrochloric or sulfuric acid has been used as 
solvent, add about 15 grams of dry ammonium nitrate or a solu- 
tion containing that amount. To the hot solution add 50 cuke 
centimeters of molybdic solution for every decigram of f,U, 
that is present. Digest at about 65° for an hour, filter, and wash 
with cold water, or preferably ammonium nitrate solution. 1 est 
the filtrate for phosphoric acid by renewed digestion and addition 
of more molybdic solution. Dissolve the precipitate on the filter 
with ammonia and hot water and wash into a beaker to a bulk 
of not more than 100 cubic centimeters. Nearly neutralize with 
hydrochloric acid, cool, and add magnesia mixture from a bur- 
ette- add slowly (about one drop per second), stirring vigorously. 
After 15 minutes add 12 cubic centimeters of ammonia solu- 
29 Bureau of Chemistry , Bulletin 107, 1907 = 3- 



6o 



AGRICULTURAI, ANALYSIS 



CITRATE-INSOLUBLE PHOSPHORIC ACID 



6l 



tion of density 0.90. Let stand for some time ; two hours is usual- 
ly enough. Filter, wash with 2.5 per cent. NH^ until practically 
free from clilorids, ignite to whiteness or to a grayish white, and 
weigh. 

65. Influence of Insoluble Silica.— It is assumed in the above 
methods that there is no more than a mere trace of soluble silica 
in the solutions of the phosphate with which the operations are 
conducted. Silica in solution (silicic acid) has also the propertv 
of forming yellow compounds with molybdate of ammonia and 
thus when present in any quantity would contaminate the precip- 
itate produced. This trouble is avoided if the acid solution of 
the phosphate is evaporated to dryness, rubbed to a fine powder 
before becoming perfectly dry, moistened with hydrochloric acid 
and taken up with water. The pasty state of the phosphoric acid 
and large quantities of soluble salts present in these cases make 
this a tedious process to be practiced only when necessary. 

66. Use of Tartaric Acid in Phosphoric Acid Estimation.— In 
the presence of iron the molybdate mixture is likely to carry 
down some ferric oxid with the yellow precipitate. To prevent 
this, and also hinder the separation of molybdic acid in the solu- 
tion on long standing, tartaric acid has been recommended. 

Jiiptner has found that the presence of tartaric acid does not 
interfere with the separation of the yellow precipitate, as some 
authorities assert.''" Even 100 grams of the acid in one liter of 
molybdate solution produce no disturbing effect Molvbdate 
solution treated with tartaric acid does not show any separation 
of molybdic acid when kept for a year at room temperatures 
The presence of tartaric acid, therefore, is highlv useful in pre- 
venting the danger of obtaining both ferric oxid and molvbdic 
acid with the yellow precipitate. 

67. Water-Soluble Phosphoric Acid.-The method of procedure 
recommended by the Association of Official Agricultural Chemists 
is as follows -' Place two grams of the .sample in a nine centi- 
meter filter ; wash with successive small portions of cold water al- 
lowing each portion to pass through before adding more, 
^ Chemisclies Central-Blatt, 1894, 2 : 813. 
" Bureau of Chemistry, Bulletin 107, 1907 : 3. 



until the filtrate measures alwut 250 cubic centimeters. If the 
filtrate be turbid, add a little nitric acid. Make up to any con- 
venient definite volume ; mix well ; take any convenient portion 
and proceed as under total phosphoric acid. 

68 Citrate-Insoluble Phosphoric Acid.— The official method ap- 
plied to samples previously acidulated is as follows : Heat 100 
cubic centimeters of strictly neutral ammonium citrate solution of 
T 09 specific gravity to 65° in a flask placed in a bath of warm 
water keeping the flask loosely stoppered to prevent evaporation. 
When the citrate solution in the flask has reached 65°, drop 
into it the filter containing the washed residue from the water- 
soluble phosphoric acid determination, close tightly with a 
smooth rubber stopper ; and shake violently until the filter paper 
is reduced to a pulp. Place the flask again in the bath and 
maintain the water in the bath at such a temperature that the 
contents of the flask will stand at exactly 65^ Shake the flask 
every five minutes. At the expiration of exactly 30 minutes 
from the time the filter and residue are introduced, remove the 
flask from the bath and immediately filter as rapidly as possible. 
It has been shown by Sanborn in his investigations, that 
the filtration is greatlv facilitated by adding asbestos pulp. 
Wash thoroughly with water at 65°. Transfer the filter and its 
contents to a crucible, ignite until all organic matter is destroyed, 
add from 10 to 15 cubic centimeters of strong hydrochloric 
acid and digest until all phosphate is dissolved ; or return the fil- 
ter with contents to the digestion flask, add from 30 to 35 
cubic centimeters of strong nitric, and from five to 10 cubic 
centimeters of strong hydrochloric acid, and boil until all the phos- 
phate is dissolved. Dilute the solution to 200 cubic centimeters. 
If desired the filter and its contents can be treated according to 
methods i', 2, or 3, paragraph 61, under preliminary treatment of 
samples containing organic matter. Mix well ; filter through a 
dry filter ; take a definite portion of the filtrate and proceed as 
under total phosphoric acid, paragraph 64. .... 

In case a determination of citrate-insoluble phosphoric acid be 
required in non-acidulated goods it is to be made by treating two 
grams of the phosphalic material, without previous washing 



i' I 



62 



AGRICUI.TURAI. ANALYSIS 



with water, precisely in the way above described, except that in 
case the substance contains much animal matter (bone, fish, etc.), 
the residue insoluble in aiiimoniuni citrate is to be treated by one 
of the processes described under i, 2, or 3, paragraph 61. 

69. Citrate-Soluble Phosphoric Acid.— The sum of the water- 
soluble and citrate-insoluble subtracted from the total gives the 
citrate-soluble phosphoric acid. 

70. Time Required for the Precipitation of Phosphoric Acid. 
—The length of time required for the complete precipitation of 
the phosphoric acid by molybdate mixture is perhaps much less- 
than generally supposed. At 65° the precipitation, as shown by 
de Roode, is complete in five minutes.^^ In a given case the 
weight of pyrophosphate obtained after fiwQ minutes was 0.0676 
gram, and exactly the same weight was found after 24 
hours. In view of these facts analysts would often be able to 
save time by omitting the delay usually demanded by the set- 
ting aside of the yellow precipitate for a tew hours in order to 
secure a complete separation of the phosphoric acid. In the 
method of the official chemists it is directed that the digestion at 
65° be continued for one hour, and this time may possibly be 
shortened with advantage. In all cases, however, where there 
is any doubt in regard to the complete separation, some of the 
molybdate solution should be added to the filtrate and, with 
renewed digestion, it should be noted whether any additional 
precipitate be formed. 

71. Examination of the Pyrophosphate.— In fertilizer control 
it is not usually thought necessary to examine the magnesium 
pyrophosphate for impurities. Among those most likely to be 
found is silica. It is proper, in all cases where accuracy is re- 
quired, to dissolve the precipitate in nitric acid, boil for some 
time to convert the pyro- into orthophosphate, and reprecipitate 
with molybdate and magnesia mixture. This treatment will sep- 
arate the silica, which remains practically insoluble after the first 
ignition. It has been observed by some analysts that the results 
obtained by the official method are a trifle too high and also that 
on re-solution the second precipitate of pyrophosphate weighs 
^^ Journal of the American Chemical Society, 1895, 17 : 43. 



DIRECT DETERMINATION OF PHOSPHORIC ACID 63 

less than the first.^^ The difference in most cases is very little, 
but It may become a quantity of consideraMe magnitude m sam- 
ples where soluble silica is found in notable quantities. The dan- 
ger of contamination with iron, alumina, and arsenic has already 
been mentioned and the precautions suggested should be careful- 

ly observed. 

72 Insolubility of Silica.-It is evident that many of the errors 
which are incident to the methods of separating phosphoric acid 
bv ammonia phosphomolybdate are due to the presence of silica 
The fact has been repeatedly pointed out by analysts. I ellet 
proposes to render the silica insoluble and thus prevent the error by 
the following procedure- The weighed phosphate is placed in a 
platinum capsule and moistened with free hydrochloric acid. The 
moistened mass is evaporated to dryness after wdnch the silica 
is no longer soluble in hot hydrochloric acid. Pellet claims that 
this method, which saves the time of a previous solution and evap- 
oration to drvness, is quite as effective as the longer metliod_^ 

73 Direct Determination of Available Phosphoric Acid.— The 
■direct determination of available phosphoric acid is not new, being 
official in several of the European countries. In this country, 
however, it has not met with favor, probably because the citrate 
method is not official here. The necessity of destroying the or- 
' ■ ganic matter before precipitating with molybdate solution pre- 
■cludes the use of the molybdate method.'' 

In 180^ Ross presented a method for the direct determina ion 
of the reverted phosphoric acid.- While the aim of this method 
met with hearty approval from the official chemists, the method 
itself did not, owing to some difficulties met with in the manipu- 
lation, and more particularly to the fact that it did not give 
results agreeing with the official method." Agreement could 
hardly be expected, because the method did not account for 
the phosphoric acid removed in the water used in washing the 
citrate-insoluble. The estimation of the available phosphoric acid 
»' Journal of the American Chemical Society, 1895, 17 :43• 
'• Annales de Chimie analytique, 1906, 11 :33i- 

»» Veitch, Journal of the American Chemical Society, 1899, 21 : 1090. 
»8 Division of Chemistry, Bulletin, 38, 1893 = I7- 
« Division of Chemistry, Bulletin 43. "894 : 7^ and Bulletin 47. 1896. 81. 



i 



64 



AGRICULTURAL ANALYSIS 



consisted in the determination of the water-soluble phosphoric acid 
by the volumetric method, as modified and carried out by Veitch ;'» 
the direct determination of the citrate-sokiblc by the citrate nietliod 
in 50 cubic centimeters of the citrate filtrate, and the determina- 
tion of that removed by washing the citrate-insoluble residue, 
using the modified volumetric method. The sum of these three 
results should equal the available phosphoric acid by the official 
method. 

It is perhaps sufficient to say that the citrate method at that 
time and later gave satisfactory results.'"' 

The two methods gave practically the same results on availables 
and on totals. The work also shows very plainly why the Ross 
method differs from the official, from 0.09 per cent, to 1.48 per 
cent, being removed and accounted for in the wash water of the 
official method that could not be accounted for by the Ross method. 
Of course, the amount removed by the wash water will vary 
somewhat in the hands of dilTerent analysts, according as they 
wash the citrate-insoluble much or little. It is the practice of 
Veitch to wash until the filtrate and washings amount to about 
250 cubic centimeters. 

A comparison of the official method with the citrate and the 
molybdate methods, precipitating with magnesia mixture and with 
molybdate solution, respectively, in the mixed filtrates con- 
tammg the water-soluble and the citrate-soluble, was undertaken. 

The method finally adopted is as follows : The water-soluble 
extracted as usual, is received in a 500 cubic centimeter flask 
graduated roughly at 250 cubic centimeters and containing from 
five to 10 cubic centimeters nitric acid. The citrate-soluble is then 
extracted as usual and the filtrate and washings received in the 
flask- with the water-soluble. After cooling, the volume is com- 
pleted, shaken, filtered, and in aliquots of 100 cubic centimeters 
the phosphoric acid is determined by one of two methods the 
molybdate or citrate, the precipitants being added directly to the 
solution without destroying the organic matter, and the precipi- 

» Journal of the American Chemical Society, 1896, 18 : 389. 

" Division of Chemistry, Bulletin 49, 1897 : 61. 



DIRECT DETERMINATION OF PHOSPHORIC ACID 



65 



• tates are allowed to stand over night before filiering. The de- 
terminations are completed as usual. 

The results by the citrate method were unexpectedly low. In 
Veitch's hands this method has always given satisfactory results, 
even on low percentages. It is probable the low results are due 
to an excess of citrate. This addition is unnecessary, and bet- 
ter results obtained when more citrate is not added, lead to the 
belief that this additional citrate is the cause of the low results. 
The results by the molybdate method are good. It was feared 
that the organic matter present would prevent the complete pre- 
cipitation of the ammonium phosphomolybdate. To insure com- 
plete precipitation the samples were allowed to stand over night 
before filtering. 

Notwithstanding the oft-repeated statement that salts of or- 
ganic acids and organic matter generally prevent the complete pre- 
cipitation of ammonium phosphomolybdate, the molybdate method 
i^ used to determine soluble phosphoric acid in the presence of 
what organic matter may be dissolved by the water used 111 the 
extraction In the Wagner method for basic slag, the precipi- 
tation is accomplished with molybdate solution in the presence of 
three grams of citric acid. Lorenz precipitates in the presence 
of two per cent, of citric acid to prevent contamination with mag- 
nesia. Jiiptner uses as much as 100 grams of tartaric acid per 
liter of molybdate solution to prevent the precipitation of iron 
' and the separation of molybdic acid." The successful use of the 
molybdate method in these cases seems to warrant the conclusion 
that we are needlessly alarmed at the presence of, at least, some 
forms of organic matter in phosphate solutions. 

The direct determination of the available phosphoric acid pos- 
sesses several advantages. Only one determination is required 
instead of two as by the present method. The probable error is 
reduced one-half. The soluble, reverted, insoluble, and total phos- 
phoric acid can also be determined in one sample and with one 
weighing, where it now takes two samples and two weighings. 
The saving 9f time effected by this method is of considerable 

« Abstract, Experiment Station Record, 1894-5, 6 : 6iu. 
3 



66 



AGRICUI.TURAI. ANALYSIS 



importance in control and in factory laboratories, whether the • 
citrate or the molybdate method is used. 

74. International Methods. — The international commission for 
the analysis of artificial fertilizers presented a report to the Fifth 
International Congress of Applied Chemistry embracing certain 
processes of analysis which are recommended for international 
adoption. ^^ The methods suggested for phosphoric acid are as 
follows : 

1. Determination of Moisture. — Ten grams of the substance 
are used ; the drying is conducted at 100° to constant weight ; sub- 
stances containing gypsum are dried three hours. 

For potash salts the regulations of the Kali syndicate at Leo- 
poldshall-Stassfurt hold good. 

2. Determination of Insoluble Matter. — Ten grams of the 
substance are used. 

A. When the substance is dissolved in mineral acids, the silica 
is rendered insoluble and the total residue ignited. 

B. When the substance is dissolved in water, the residue is dried 
at 100° to constant w^eight. 

. 3. Determination of Phosphoric Acid. — A. Method of mak- 
ing the solutions. 

1. In the case of water-soluble P^O^, 20 grams substance 
are to be agitated for 30 minutes with aboui 800 cubic centimeters 
water in a liter bottle and then filled up to 1000 cubic centimeters. 
The solution of so-called double superphosphates must be boiled 
with HNO3 previous to precipitation of the PoO.„ whereby any 
pyrophosphoric acid \\h\Q\\ may be present is converted into 
orthophosphoric acid. 

For every 25 cubic centimeters of solution of double superphos- 
phate, 10 cubic centimeters concentrated HXO.^ must be used. 

When the amount of citrate-soluble phosphoric acid in super- 
phosphates is required, the determination must be made accord- 
ing to Petermann. 

2. For total phosphoric acid five grams of the substance are 
boiled with aqua regia or 20 cubic centimeters ^HNO..^ and 50 

*^ Proceedings of the Fifth luternatioiial Congress of Applied Chemistry, 
Berlin, 1903, 1 :228. 



INTERNATIONAL METHODS 



67 



grams concentrated tLSO. for 30 minutes and filled up to 500 

"f Tot"™". P.a in ...g PI.«.P.«.«. ."e "-»'. «>■■"■ '»■ 

pears to contain coarse particles, is passed through a two 
millimeter sieve ; the portion which remams behmd is sligh ly 
ruled The d;termiLtion of P.O. is made in the portion which 
passes through the sieve, the result being calculated so as to m- 
clude the portion which remains behind. 

(a) Citric acid soluble P.O,. 

Five grams of the substance are placed in a 500 cubic centi- 
meter flask with five cubic centimeters of alcohol to prevent bak- 
..g and shaken with two per cent, citric acid solution for one half 
hour at I7°.5 in a rotary apparatus which makes 30-40 revolutions 

per minute. 

(b) Total P.O^-'' , . ,; 

Ten -rams of the substance are placed in a 500 cubic centi- 
meter flask, thoroughly mixed with a few cubic centimeters of 
water and boiled for 30 minutes with 50 cubic centimeters concen- 
trated H,SO„ the flask being frequently shaken. 

. B Analysis of the Solutions. 

I.' Molybdate method according to Fresenius and P. Wagner. 

2. Citrate method. 

' 1.. Free acid. . . , 

(a) Total free acid: The aqueous solution A i is. titrated 
with a solution of NaOH, using methyl orange as an indicator. 

(b) Free phosphoric acid: An alcoholic solution is used for 
making a gravimetric determination. 

4 Determination of Ferric Oxid and Alumina. 

This determination must be made either according to the meth- 
od of Eugen Glaser- as improved by R. Jones" or in the case 
of the determination of alumina, according to Henn Lasne. The 
method adopted must be mentioned. 

« When a <leterrainatio.i of the fine dust is to be ma<le, a sieve of 0.17 

"''"'"zluschHH"fuf a,%"::lndte Ounne. ,889. 2 : 636 ; Die landwirl- 
^''-':^^^^'^^S^ C,?e\nS .S?i% : 3; Zeitschrift fUr ana.yt- 

ische Cheniie, 1891, 30 '• 743- . . -, -r, •« -.q^x/; r-il \^ 116 ixl' 

^■> Bulletin (le la Soci^te chiniKiue de Paris, 1896, [3], 15 M^^ 237, 

Cheiuiker-Zeituiig Repertorium, 1896, 20 47, ^5- 



I 



68 



AGRICULTURAL ANALYSIS 



METHODS FOR PHOSPHORIC ACID USED IN NORWAY 



69 



75. Methods of the German Experiment Stations. — The pro- 
cesses adopted by the nnioii of the German agricuUural experi- 
ment stations are based on the general methods of procedure 
already outlined as is seen from the following resume, '''^ The 
sample containing the phosphoric acid is dissolved in aqua regia 
in. the proportion of five grams of the sample to 50 cubic centi- 
meters of the acid, made by mixing three parts of hydrochloric 
acid of 1. 1 2 specific gravity with one part of nitric acid of 
T.25 specific gravity or 20 cubic centimeters of nitric acid of 1.42 
specific gravity with 50 cubic centimeters of sulfuric acid 
of 1.8 specific gravity. VVith the latter reagent the boiling is con- 
tinued for 30 minutes. The phosphoric acid is then determined 
by the direct (Bottcher) method.^^ 

76. Water-Soluble Phosphoric Acid.— The soluble acid in acid 
phosphates is extracted by treating 20 grams of the sample in a 
liter flask with 800 cubic centimeters of water for 30 minutes with 
vigorous shaking, filling the flask to the mark, shaking and filling. 
A mechanical shaker is recommended with a vibration or rotation 
of 150 turns a minute. The acid is determined in an aliquot part 
of the filtrate by the magnesia citrate method. Solutions of double 
acid phosphates are boiled with nitric acid before treatment in 
order to bring all the phosphoric acid in the ortho form. When 
required the content in water-soluble and citrate-soluble acid 
must be 'returned separately and not in one figure as citrate-solu- 
ble acid. It was decided that the new Wagner method for de- 
termining citrate-soluble acid in Ijasic slag should be adopted. 
This method is given in another paragraph, and it is not to be 
applied to other phosphatic materials such as bone-meal. 

77. Official Norwegian Methods.— The Director of the Chemical 
Control Station of Norway, expresses the opinion, that for Nor- 
wegian, Swedish, Danish and German conditions, the quantities 
of material required by the American methods for the determina- 
tion of phosphoric acid, notwithstanding their analytical exact- 

*^ Die landwirtschaftlicheii Versuchs-Stationen, 1904, 60 : 371. 

*^ Die landwirtschaftlichen Versuchs-Stalionen, 1903-4, 59:313; 1904, 
60:221. 



ness are insufficient.^^ In those countries are found many, m part, 
poorly pulverized, and badly mixed manures, such as ammonium- 
superphosphate, potassium-superphosphate, and potassium-ammo- 
nium-superpho.phate, and these can not usually be so well pul- 
verized and mixed that one can secure a true average sample of 
from two to two and five-tenths grams. Care in the analysis is use- 
less when the material employed does not represent the average 
conditions of the materials investigated. Therefore, in the coun- 
tries named, often from 10 to 20 grams, and almost never less 
than five grams of substance are used in the preparation of the 
solutions, except, for instance, in the determination of nitrogen 
and reverted phosphoric acid. 

78 Methods for Phosphoric Acid Used in the Norway Stations. 
-I Description of the Method for Total Phosphorie ActcL-¥oT 
determining the phosphoric acid in bone-meal, fish-guano, and 
superphosphates, five grams of the substance, with 20 cubic 
centimeters of nitric acid of t.42 specific gravity, and 50 cubic 
centimeters of -sulfuric acid of 1.8 specific gravity, are boiled ha f 
an hour in a half liter flask, diluted with water, and after cool- 
ing made up to the mark. Fifty cubic centimeters of the fiUrate 
are made alkaline with ammonia, then acid with nitric acul, pre- 
cipitated with 50 cubic centimeters of molybdic solution for every 
one-tenth gram of phosphorus pentoxid present, heated over 
the water bath for one hour, and allowed to stand 12 hours, 
when the supernatant liquid is separated by decantat.on, the pre- 
cipitate washed thoroughly with dilute molybdate solution (1:4). 
dissolved in warm dilute ammonia, and the filter washed with hot 
water The ammoniacal solution is neutralized with hydrochloric 
acid cooled, mixed, drop by drop, with constant stirring, with 
from 10 to 20 cubic centimeters of magnesia mixture, and 
after a quarter of an hour one-third the volume of 10 per cent, 
ammonia is added. This, after standing two hours, is filtered 
washed with five per cent, ammonia until the disappearance of 
the chlorin reaction, dried, burned in an open crucible over a 
bunsen, and finally, for a quarter of an hour, in a covered cru- 
cible over the blast. 

<» Division of Chemistry, Bulletin 47, 1896 : 85. 

« Solberg, Division of Chemistry, Bulletin 47. '896 • »3- 



70 



AGRICULTURAI. ANALYSIS 



m 



>t 



2. Water-Soluble Phosphoric Acid. — To 20 grams of the 
substance in a liter flask, are added 800 cubic centimeters of water, 
shaken every 15 minutes for two hours; the volume is made 
up to the mark and the phosphoric acid in 50 cubic centimeters 
of the filtrate, equalling one gram substance, is determined as un- 
der total. 

3. Reverted Citrate-Soluble Phosphoric Acid. — Two and five- 
tenths grams substance are rubbed up with water, washed upon 
the filter with about 100 cubic centimeters of water, the residue 
on the filter washed into a flask with a part of the measured cit- 
rate solution, and digested one hour at from 35° to 40° with 200 
cubic centimeters of Petermann's citrate solution. The water and 
citrate extracts are made up to a quarter of a liter each, and 
the phosphoric acid determined in from 25 to 50 cubic centime- 
ters, according to the quantity present. 

Solutions. I. Molyhdate Solution. — Three hundred and seven- 
ty-five grams of ammonium molyhdate are dissolved in two and 
five-tenths liters of water, and the solution poured into two and 
five-tenths liters of nitric acid of 1.20 specific gravity. 

2. Magnesia Mixture. — Two hundred and seventy-five grams 
of crystallized magnesium chlorid and 350 grams of ammonium 
chlorid are dissolved in 3250 cubic centimeters of water and filled 
up to five liters with ammonia of 0.96 specific gravity. 

3. Petermann's Solution. — One kilogram of citric acid is dis- 
solved in about two liters of water and 1350 cubic centimeters of 
ammonia of 0.925 specific gravity and filled up with water to 
5750 cubic centimeters. The solution then has a specific gravity 
of 1.09; 300 cubic centimeters of ammonia of 0.925 specific grav- 
ity are added. 

79- The Molybdic Acid Method as Practiced by Members 
of the Union of the German Experiment Stations.— The method 
adopted by the German experiment stations is essentially that 
used at Halle.^<> The samples are brought into solution ^in the 
following way : For the estimation of phosphoric acid in bone- 
meal, fish-guano, flesh preparations and raw phosphates, and the 
total phosphoric acid in superphosphates, five grams of the sample 
^ Die landwirtschaftlichen Vcrsuchs-Stationen, 1891, 38 1306. 



THE MOLYBDIC ACID METHOD 



71 



.re dissolved in 50 cubic centimeters of aqua regia, made of three 
oartfof hydrochloric acid of 1.12 specific gravity and one pa 
tri acid of 1.25 specific gravity, or the solvent may be mad 
of a mixture of 20 cubic centimeters of mtric acid of 142 

r :iS ■„ J^up t tl. a liter a„. «H„.d^ Fi.tv c„«c 

, TZl at ^o" in a water bath and, after cooling, filtered, .o 
Ihlfa^; HtrafpoLible of the precipitate is collected upon the 

'''^,::^ :::Z^Lt:i::^^y -antation in the fias. 

• . ;r wkh ^o cubic centimeters of molybdic solution 
tune times with 20 ^^^^ ^^^^ 

diluted with one volume of water and tne niier w 
w h the same quantity of liquid ^he funnel wityhefiUe^s 
immediately placed upon the flask and the portion of the prec.p. 
tT collected in the filter dissolved in five per cent, ammoma, 
: chtSy accomplished by throwing ammonia upon :^^^^^^^ 
. v.ash bottle Afterwards the filter is washed with a sufticient 

.nd treated drop by drop, with constant stirring, with 20 cubic 
and treatea, cirop y 1 , rrinallv 2=; cubic centimeters of 

centimeters of magnesia mixture. Finally 2^ cud 
dilute ammonia solution are added, the precipitate is not shaken, 
and after two hours is filtered through a gooch. 

For the filtering of the ammonium magnesium phospha e by 
the n o lybdic meth'od, freshly prepared felts are always employed 
s^nce the remarkably fine crystalline precipitates will pass hrough 
a Iter which has once been used It is fiecessary als th^ 
special precautions be taken in the ignition T'- ;™;;^^ 
should be heated in a platinum cap, which ha. the purpose ot 
ot cting the contents of the crucible from the access of redu- 
ci, t g^se's during the ignition. After redness has been reached 



72 



AGRICUI.TURAI, ANALYSIS 



the cap can be removed and tlie crucible transferred to a blast 
where it is strongly ignited for lo minutes before weighing. 
The precipitate should be pure white. 

The molybdic solution is prepared as follows : One hundred 
and fifty grams of ammonium molybdate are dissolved in a liter 
of water, and after the solution is completely cooled, poured into 
a liter of nitric acid of 1.2 specific gravity. 

80. Estimation of Soluble Phosphoric Acid. — i. The extraction 
of the superphosphates is made as follows: Twenty grams of 
the superphosphates are placed in a liter fiask with 800 cubic centi- 
meters of water and shaken continuously for 30 minutes. The 
fiask is then filled with water to the mark and the whole again 
thoroughly shaken and filtered. For shaking, a machine is re- 
commended, driven by hand or water power. The normal rate 
of the machine is fixed at 150 turns per minute. 

2. The solution of double superphosphates, obtained as above, 
must be boiled with nitric acid before the precipitation of the phos- 
phoric acid in order to convert any phosphoric acid present as 
pyrophosphoric into tribasic phosphoric acid. For each 25 cubic 
centimeters of the superphosphate solution 10 cubic centimeters of 
concentrated nitric acid are added and the mixture boiled. 

3. The precipitation of the phosphoric acid is conducted by 
the molybdate method as usually practiced. 

4. For the estimation of iron and alumina in each of the su- 
perphosphates the Glaser alcohol method is recommended pro- 
visionally. A description of this method is given further on. 

81. The French Official Method.— For the purpose of securing 
the most appropriate method of analysis the materials to be ex- 
amined are divided by the French authorities into the following 
classes :^^ 

These groups are : 

1. Mineral phosphates, consisting of tricalcium phosphate 
more or less mixed* with carbonate of lime, silicious matters, oxids 
of iron and alumina, etc. 

2. Bone phosphates and bone black. 

3. Phosphates in manures, poudrettes and guanos. 

^'Sidersky, Analyse des Engrais, 1901:54; h^ Sucrerie indigene et 
colomale, 1897, 50 : 382. ^ 



THE FRENCH OFFICIAL METHOD 



73 



4. Superphosphates, precipitated (reverted) phosphates, am- 
monia-magnesium phosphates. 

5. Phosphatic slags. 

In the first class the phosphoric acid is determined by direct 
precipitation by the citrate method. 

In the second and third classes previous to the separation of the 
phosphoric acid the organic matter is destroyed after treatmg 
with some slaked lime to prevent the organic matter from reduc- 
ing any phosphate. After the reduction of the organic matter 
the process is continued as in the first class. 

In the fourth class the precipitated (reverted) phosphoric acid 
is dissolved in ammonium citrate. About 0.75 ^^^^ ^^ the sample 
is rubbed in a mortar with a few drops of the citrate solution 
and the paste washed into a flask of 150 cubic centimeters capac- 
ity with 60 cubic centimeters of the citrate of ammonia solution 
and digested with frequent shaking for 12 hours. The flask is 
subsequentlv filled to the mark and, after shaking, the contents 
are poured on a filter, and in too cubic centimeters of the filtrate, 
representing 0.5 gram of the sample, the phosphoric acid is sepa- 
rated as above. 

The total phosphoric acid is determined as in the first in- 
stance. 

In the fifth class the phosphoric acid is separated as usual 
after solution in hvdrochloric acid and not nitric. When the 
siags are verv rich in lime it is advisable to dissolve first in acetic 
acid and separate the greater part of the lime as oxalate before 
dissolving the phosphoric portion of the slag in hydrochloric acid. 
The molybdate method is also used ofificially by the French 
chemists in harmonv with the usual directions. 

The methods employed are so nearly like those already described 
that their repetition is not deemed necessary. The determination 
of the degree of fineness of the sample is properly regarded by 
the French chemists as of great importance. 

In the case of natural phosphates and slags it is advised that 
the sample be separated by a sieve of 0.17 millimeter mesh. At 
least 90 per cent, of the sample should pass such a sieve. 



I 



74 



AGRICULTURAL ANALYSIS 



m 



•I 



^1 



82. Swedish Official Method for Determination of Phosphoric 
Acid.^- — The Swedish chemists determine phosphoric acid in fer- 
tihzers both by the molybdate and the citrate methods. These 
methods carefully conducted according to the directions given 
below, give very concordant results. In doubtful cases the former 
method is taken as the deciding one, it having proved by long 
practice to give very satisfactory results. 

Reagents for the Molybdate Method. — i. Molybdie Solution. — 
Prepared by dissolving 100 grams of finely powdered molybdie 
acid with heat in 400 grams of eight per cent, ammonia of 0.967 
specific gravity and pouring the solution into 1500 grams of nitric 
acid of one and two-tenths specific gravity ; or else by dissolv- 
ing 150 grams ammonium molybdate in one liter of hot water, and 
pouring the solution into one liter of nitric acid of 1.2 specific 
gravity. Prepared in this way, the molybdie solution will con- 
tain, in the former case, five per cent., in the latter case, from five 
to six per cent, of molybdie acid, and 100 cubic centimeters of it 
are required for precipitating one-tenth gram of phosphorus 
pcntoxid. 

2. Magnesia Mixture. — Prepared with no grams of crystal- 
lized magnesium chlorid, 140 grams of ammonium chlorid, 700 
grams of eight per cent, ammonia of 0.967 specific gravity and 
1300 grams of distilled water. The mixture is filtered after a few 
days, if necessary; 10 cubic centimeters are required for precipi- 
tating one-tenth gram of phosphorus pentoxid. 

3. Ten per cent, ammonia of 0.959 specific gravity. 

petenninations: (a) Water-Soluble Phosphoric Acid. — i. 
Preparation of the Aqueous Solution. — Of superphosphates and 
other fertilizers containing water-soluble phosphoric acid, 20 
grams are treated with water in a mortar ; lumps are crushed 
lightly but completely with the pestle without pulverizing 
finer ; the whole mass is then washed into a graduated flask hold- 
ing one liter, which at once is filled up to the mark. The volume 
taken up by the residue insoluble in water is left out of considera- 
tion in the calculation. After standing in the flask ( which is 

" OfTicial Swedish Methods Translated for the Author by F. W. Well. 



SWEDISH DETERMINATION OF PHOSPHORIC ACID 



75 



occasionally shaken) at the ordinary temperature of the room for 
two hours, the mixture is filtered. 

2 The Deternnnation.-ro 25 cubic centimeters of the super 
pho;phate solution thus prepared (or a ^-f^>;/^J f^ 
sample equal to one-tenth gram phosphorus pentoxid) add a 
quantity of molybdie solution sufficient for complete precipitation, 
leave standing for four hours in a beaker covered with a watch- 
es -decant the solution through a small filter, wash the pre- 
cipita'te first by decantation, then on the filter, with a --ture con- 
tahnng 100 parts molybdie solution, 20 parts nitnc acul o 
I 2 specific gravity, and 80 parts water, until a few drops 
,ut into alcohol, to which some dilute sulfuric acid has been added 
So not any longer cause turbidity, ^he ^oly chc p^^^^ 
now washed with a little water from the filter into a beaker 
and particles adhering to the filter are dissolved ^v a ho mix^ 
ture of one part ammonia and three parts water, which is allowed 
to flow into the beaker till the precipitate is finally completely 
dissolved in it. To the clear solution add dilute hydrochloric acid 
while stirring till the yellow precipitate formed by the acid is no 
longer immediately dissolved; then add from six to eight cub c 
centimeters of ammonia through the filter. The volume o the 
solution is not to exceed 75 cubic centimeters. It is cooled com- 
pletelv and one cubic centimeter of magnesia mixture is added 
from' a burette for every centigram of phosphorus pentoxid 
which it is expected to contain, and finally one-quarte. of 
:; volume of ammonia is added. The precipitate may be filtered 
after four hours, and washed on the filter, preferably by means of 
suction, with a mixture of one part ammonia ^-\f^[''^^^^^^ 
water till the filtrate is entirely free from chlorin. After dr>ing 
heat the precipitate, first gently, then stronger, and finally with a 
blast for a few minutes and then weigh it. . , , , .. 

Treated with hvdrochloric acid it must leave no insoluble residue 
(SiO^), nor should hydrogen sulfid cause any precipitation in the 

solution thus formed (M0O3). , , , r^^ ,u^ 

(b) Total Phosphoric Acid.-i. In Superphosphates.^Vov the 

determination of total phosphoric acid, treat a weighed quantity 

of the superphosphate with nitric acid, if necessary to bring a dif- 



76 



AGRICUI.TURAI. ANALYSIS 



ficultly soluble residue into solution, with addition of hydrochloric 
acid, or of potassium chlorate, to destroy organic matter present. 
Dilute the solution to a definite volume and determine the phos- 
phoric acid in a measured quantity thereof, as directed under (a) 
2; if hydrochloric acid or potassium chlorate be applied in the 
preparation of the solution, however, the determination of the 
phosphoric acid must not be made till the measured quantity 
has been repeatedly evaporated to dryness with concentrated nitric 
acid. 

2. In Bone-meal. — Destroy organic matter in five grams of the 
sample by ignition, dissolve the residue in nitric acid, filter from 
the insoluble residue, dilute the filtrate to half a liter, and deter- 
mine the phosphoric acid as directed under (a) 2 in an aliquot 
part containing about one-tenth gram phosph.oric pentoxid. 

3. In fish- guano (and other fertilizing materials of organic 
origin). — The organic matter cannot here be removed by sim- 
ple ignition, as in this way a loss of phosphorus may take place ; 
it is therefore destroyed either in the wet way by nitric acid and 
potassium chlorate, or in the dry way by fusion with a mixture of 
potassium nitrate and sodium carbonate, otherwise the procedure 
is as in (b) I. 

4. In Mineral Phosphates. — Determine the phosphoric acid in 
a solution obtained by nitric acid ; organic matter if present is 
destroyed preferably in the wet way. 

5. In Basic Slag. — Dissolve 10 grams of powdered slag by 
treating it with 100 cubic centimeters of hot fuming hydrochloric 
acid ; wash the solution ir.to a graduated half liter flask, fill to 
the mark, shake well, and filter. Determine the phosphoric acid 
in 25 cubic centimeters of the clear filtrate, according to (a) 2, 
after having first, however, evaporated the solution to dryness 
and then at least three times evaporated the residue to dryness 
with concentrated nitric acid. 

83. Method Employed by the Royal Experiment Station of Hol- 
land. — A. Soluble Phosphoric Acid.^^ — The necessary reagents 
are : 

(i) Molybdate solution, made by dissolving 150 grams of am- 

Metlioden van Onderzoek aan dc Rijkslandbouwproefstatiqns, 1893 : 4. 



53 



METHOD EMPLOYED BY HOLLAND 



77 



.nonium molybdate in a liter of water and pouring the solution 
into a liter of nitric acid of 1.20 specific gravity. 
(2^ \ 10 per cent, solution of ammonium nitrate. 
3 Strong and dilute ammonia, the latter being between two 
and five-tenths and three per cent, and of 0.988 specific gravity 

(4) Magnesia mixture made by dissolving no grams of crxs- 
t^d it d magnesium chlorid, 140 grams of ammonium chlond and 
^oo cubic centimeters of ammonia of 0.96 specific gravity m 
water and bringing the solution to two liters. 

( O Ammoniacal citrate solution, made by dissolving 500 grams 
of citrit acid in a liter of water, and mixing with four liters of 
10 per cent, ammonia of 0.96 specific gravity. 

Mam>./a/ion.-Place 20 grams of the substance -^-J^^^^ 
togethef with some cold distilled water or pure ^-^^J^^^^^ 
and decant the water and suspended matters into a liter flask 
Xftr th has been repeated several times, rub up the residual 
mass and wash it all into the flask. Fill up to about 900 cubic 
^ZZt^t^X allow to stand two hours (24 hours in the case 
TZur,^.o.,Xr..^s with more than 22 per cent, of soluble phos- 
horic acid) • shaking repeatedly, or shaking continuously, for 
h If an ht : Fill up to ?he liter mark and filter through a dry 
Suer Add 100 cubiJ centimeters of molybdate solution for each 
to mifligrams of phosphorus pentoxid present, to portions o 
Tor o cubic centimeters for each determination, warn, to about 
8^ for an hour, filter, and wash the precipitate with the ammo- 
nhin it solution. Add a little molybdate solutioi.^ to the 
fi "ate warm, and, if a fresh precipitate be observed, it is to be 
aid d to he first. The precipitate is dissolved in ammonia and 
Kdroclric acid carefully added until the precipitate caused by 
tX slowly redissolves on stirring. The phosphoric acid is 
prStatd from the clear liquid, which is still ammoniacal, with 
Lgn sJl n^ixture, using 10 cubic centimeters for eac - -Ih- 
o-rams of phosphorus pentoxid present. This is added, d op by 
drop an 1 the liquid kept stirred during the addition. Allow to 
Ind" e two hours, filter, wash with dilute ammonia dry, 
d I ite a first with a very small flame, and finally with the 
t^f^^^^^ ni a Rossler furnace. To insure burning to white- 



I 



78 



AGRICULTURAL ANALYSIS 



r.^ TM THT? MOLYBDATE METHOD 
SOURCES OF ERROR IN THE MOi.^-^ 



79 



ness, nitric acid may be used, but not more than one or two 
drops. 

B. l^otal Phosphoric Acid. — (i) For bone and flesh-meal, 
fish-guano, and similar fertilizers the reagents necessary are the 
same as before. 

Carefully burn five grams to ash, boil the ash for half an hour 
with nitric acid of 1.32 specific gravity, dilute with water, and, 
after cooling, dilute to 500 cubic centimeters. Filter through a 
dry filter and add 100 cubic centimeters of the molybdate solution 
for each 100 milligrams of phosphorus pentoxid present to 50 
cubic centimeters of the filtrate. Treat further as before described. 

(2) Phosphates, guanos, bone-black, etc. 

One gram of substance, after powdering, and, if necessary, 
igniting, is covered with four cubic centimeters of hydrochloric 
acid of 1. 1 3 specific gravity and a little water and heated for an 
hour and a half. Evaporate to dryness without filtration, making 
repeated additions of nitric acid until no more vapors of hydro- 
chloric acid are evolved. Boil the residue with nitric acid, cool, 
make up to 100 cubic centimeters with water, and shake. Filter 
and treat 50 cubic centimeters of the resulting solution by the 
molybdate method and proceed further as before described. 

84. Sources of Error in the Molybdate Method. — When con- 
ducted with proper care, the gravimetric molybdate method is one 
of the most exact processes known to analytical chemistry. 

There are, however, some sources of error in the process which 
should be avoided as carefully as possible or taken into account. 
. I. Error Due to Occluded Silica. — When silica passes into 
solution in the original sample, and this may ])e the case especially 
with mineral phosphates, it may appear both in the yellow pre- 
cipitate and in the final magnesium pyrophosphate. In all such 
cases the residue, after ignition, should be dissolved in hydro- 
chloric acid and any insoluble residue weighed as silica and de- 
ducted from the first weight. If the silica be removed by evap- 
orating the solution of the original material to dryness, and 
igniting to destroy organic matter, care must be taken to recon- 
vert all phosphoric acid into the ortho form by long boiling with 
nitric acid before precipitation. 



Another ,„.!»<, of ,v„icV,„e »">\ rl/^oruTo "he" r 

vapors are ^f/^'*" .^._.Onlv in rare cases will arsenic be 

2. hrror Due to Arsenic ^ -V . .^ ,„„ of pyritic phos- 

found in phosphatic fertihz.ng "^^^^^^'^^^^^n in such 

''•-^-^^"^ct;;sSirh7^oXicI'd: U a,., regla 
a case is best accompUshea n n> reneated evapora- 

h, „.., an nitric acid ''«''^^ ^J^^ctn Jc f reprcc.pL.d 

in the hot ciume iiyu.^^ , , ,, • Thp dani?er of contami- 

. Frror Due to Ocelnded Magnesia.— i\^^ clanger o 

J,f Tt. hnal preci.^^^^^ ^^Xr:. the p^i "^e 

s;r:;:^s::^^;-nist.ns^^^^^ 

Lorenz states that this -"^^ °^ ^7° ^ ^^^.^f/^o he solution » 
the addUio.. of two ^-^.;[^ir^J,^o. of some 
Without the addition °J ;'*";,;' Vstronglv ammoniacal solu- 
n.agnesia with the phosphate, at leastm rong . ^^^^^^^^ 

tions. cannot be avoided even by ^^^ ^^^ ,^ ^^..^ in the 
addition of the magnesia mixture. Ihe citnc 
common form of ammonium citrate solutioi. 

^ ,. Error Due to ^t'''^^' Vofat^st^^^^^^^^^ 

:U in the loss of Phos^io^^^^ ^^ "^^r Jof ^ ^Z 
nesia-covered crucible l''\°f " ^J'^f^.^t Of course, the pres- 

::vr,:rrr„r^*':t;Hri;:,u-onis,ia,.,c,o.s.nr..., 

pheck 

M zeitschrift fur analylische Chemie, 1893. 32 : 64_ 

.3 Journal of the American Chemical Society, 1894, 16 • 289. 

Uted and Abridged by K. P. McElroy. 



N 



80 



AGRICULTURAL ANALYSIS 



The following course of procedure in the determination of 
[jjiosphoric acid can be recommended to avoid or correct this 
error : 

Separate the phosphoric acid in the form of the yellow precip- 
itate and wash this latter in the usual way. Too high a heat 
should not be employed, nor should the solutions be allowed to 
stand too long, lest excess of molybdic acid separate. Dissolve 
the phospliomolybdate in 100 cubic centimeters of cold two and 
five-tenths per cent, ammonia and add as many cubic centi- 
meters of the usual magnesia mixture (55 grams magnesium 
chlorid and 70 grams ammonium chlorid dissolved in a liter 
of two and five-tenths per cent, ammonia) as there are centi- 
grams of phosphorus pentoxid present. Addition should not be 
made faster than 10 cubic centimeters per minute. Stir during 
the addition. After the precipitation stir briskly once more and 
allow to stand at least three hours. Wash with two and five- 
tenths per cent, ammonia till the chlorin reaction disappears, dry 
tlie filter, and introduce into a well cleaned crucible which has 
been thoroughly ignited. Place the lid at an angle, carbonize 
the filter, and gradually raise the heat, though not higher than 
a medium red heat, till the pyrophosphate becomes completely 
white. When this happens bring the blast into action and ignite 
to constant w^eight. The weight finally accepted must not chanee 
even after half an hour's ignition. Upon this requirement espe- 
cial stress must be laid. Pure magnesium pyrophosphate does 
not sufi'er any loss even after several hours' ignition, nor does 
a good platinum crucible. To the weighed amount of pyrophos- 
phate add the correction given in the table. For example, if th.e 
weight be 250 milligrams, the correction to be added is four and 
two-tenths milligrams, and the correct weight is then 254.2 milli- 
grams. Multiplication of the sum by sixty-four gives the amount 
of phosphorus pentoxid in the weight taken for analysis. 

When phosphoric acid is to be estimated as pyrophosphate it 
must always be first separated as molybdate, even when the orio-- 
inal solution contains no bases capable of forming insoluble phos 
phates, as otherwise these corrections will not be applicable. 



MODIFICATION OF JORGENSEN 



8 



Using these corrections, the estimation of phosphoric acid be- 
comes one of the most accurate of known analytical methods. 
Correction for Phosphoric Acid Determination. 



Found, 

Mg2P207 

in grams. 
O.IO 
O. 12 
0.14 
0.15 

o. 16 

0.17 

0.18 
0.19 
0.20 
0.21 
0.22 



Lost, 
milligrams 

MgoP^O?- 
0.6 

0.8 

1.2 

1.4 

1.6 
2.4 
2.6 
3.2 

3.5 
36 

3.8 



Found, 

MgoPoO; 

in grams. 
0.24 
0.25 
0.26 
0.27 
0.28 
0.29 
0.30 
0.31 
0.32 

0.33 
0.34 



L,osi. 
milligrams 
MgaPaO;. 

4.0 

4.2 

4.6 

5.0 • 

6.1 
6.8 
7.6 
8.6 
9.6 
10.6 



85 Modification of J.rgensen.-Jorgensen has submitted to a 
renewed detailed study the standard methods of precipitation 
of phosphoric acid as magnesium ammonium phosphate for the 
purpose of determining whether any errors have crept into the 
u.ual methods.- He used as the basis of his test for accuracy bv 
preference a preparation of sodium ammonium phosphate in a 
crystalhne state, NaNH.HPOJLO. He selected this salt as 
the one best suited for testing the accuracy of the method ana 
the puritv of reagent because it can be prepared easi.y m a state 
of puritv'by recrvstallization out of ammoniated water, the crys 
tals are' subsequ'entlv exposed in the air until <lry. It is also a 
sal't which has little tendency to efflorescence, and its purity can 
be determined without reference to its phosphoric acid content 
bv determining the loss of weight upon ignition an.l by dc-ter- 
raining its content of ammonia. If these two determinations show 
a pur; salt the content of phosphoric acid may be left out of con- 
sideration, since this is the material upon which methods and soa,-- 

lions are to be tried. . 

Aside from the variation in the standard of comparison, there 
is little new in J^rgensen's work. He makes a few changes in 
the composition of preparations which he uses, btit the change in 
no case is great enough to introduce any appreciable difterence in 
the manipulation. 

56 Zeitschrift fUr aiialytischeChcmie, 1906, 45 . 273. 



i 



82 



AGRICUI.TURAI. ANAI^YSIS 



Jorgensen calls especial attention to the tests which he has 
made on the influence of impurities in the phosphatic materials 
which are to be determined, and especially of the maximum quan- 
tities of silica, iron, calcium, aluminum, or salts thereof, which 
may be present without interfering with the accuracy of the pro- 
cess. He also uses a concentrated molybdate solution of which 
about 61 cubic centimeters are necessary for the precipitation of 
0.2 gram (P^O^) on the supposition that one part of phosphorus 
is best precipitated in the presence of about 12 parts of molyb- 
denum. 

In the application of the method for fertilizing materials Jor- 
gensen prefers that they should be brought into solution either 
with hydrochloric or sulfuric acids, hydrochloric preferred. For 
the conversion of the pyrophosphates into phosphates, however, 
nitric acid is necessarv. If the solution contains about 0.2 of 
pyrophosphoric acid in 50 cubic centimeters, it should be boiled 
with 10 cubic centimeters of nitric acid of a specific gravity of 
1.4 for a quarter of an hour, or 2.5 of nitric acid of the samel 
strength for half an hour, or 1.25 cubic centimeters for an hour. 
In the precipitation of the phosphoric acid in the fertilizers, if 
ferric oxid is present not exceeding in quantity 0.22 gram, 
aluminic oxid in quantity not exceeding o.ii gram, calcium oxid in 
quantity not exceeding 0.42 gram, and silica in quantities not ex- 
ceeding 0.17 gram, these bodies do not exert any injurious effect. 
The molybdate precipitate is washed about 10 times by decanta- 
tion with from 20 to 25 cubic centimeters of a nitric acid solu- 
tion of ammonium nitrate consisting of about one per cent, of 
nitric acid to about five per cent, of ammonium nitrate in too parts 
of the solution, and afterwards the precipitate is dissolved in a 
measured quantity of 2.5 per cent, of ammonia in such a way 
that about 100 cubic centimeters of the solution are used for 
each 0.2 gram phosphoric anhydrid, with similar quantities of 
phosphoric acid and correspondingly less quantities of the sul- 
phate. If the filter is not considered well washed, a small quan- 
tity of water may be used afterwards for this jnirpose. The solu- 
tion is then heated in a covered beaker until bubbles of steam 
begin to escape, and drop by drop treated with a neutral mag- 



I 



PHOSPHORIC ACID DETERMINATION 



83 



nesium solution of which from 15 to 20 cubic centi- 
meters are required for each 0.2 gram of phosphoric anhydrid 
present After the addition of the magnesium solution and dur- 
ing the cooling it is desirable to frequently shake the vessel con- 
taining the precipitate, especially if the precipitate has changed 
into the dense, crystalline form, which is apt to be the case for 
the addition of the magnesium mixture has been slow and there 
is not a sufficient excess of ammonia. The ordinary stirnng ap- 
paratus which is used can give valuable service at this point. 
The filtration of the precipitated phosphoric acid should not take 
place until after four hours' standing. A longer time than four 
hours does not have any influence upon the results. After the 
collection of the material in the filter it is washed with 2.5 per 
cent of ammonia. It is very convenient to have the bottom of 
the crvstal covered with precipitated platinum, since m this case 
the heating over a blast-lamp is unnecessary, the ordinary heating 
over a common burner being sufficient. For conversion the factor 
0.63757 is used. (Log. 0.80453^1). 

86 Influence of Aluminium, Magnesium and Calcium upon the 
Phosphoric Acid Determination. -In solutions containing alumin- 
ium iron, magnesium and calcium in which phosphoric acid is 
to be determined, the influence of these bases upon the deter- 
mination must not be neglected. Neubauer has called attention- 
to this point, especially in connection with the determination of 
phosphoric acid in the hvdrochloric acid solutions of soils.-^ 
The well known fact that the chlorid of lime and aluminium 
* at moderate heating in the air and in water pro.luce .nsohible 
oxids with which the phosphoric acid as an insoluble sulfate is 
entangled is well known. The chlorids of alkalies, however, 
are not changed bv this heating, and this ditTcrence in deport- 
ment is the principle upon which Neubauer bases his observations. 
Where onlv potassium and phosphoric acid are to be determined 
in a hydrochloric acid solution, for instance, of a soil, Neubauer 
uses the following process: 

A volume of the solution corresponding to 25 grains of the 
original substance (soil) is evaporated to dryness in a platinum 
•■" Die lan(lwirtschaftlichen Versuclis-Stationen, 1905-6, 63 ; 141- 



I 



84 



AGRICULTURAL ANALYSIS 



PHOSPHORIC ACID DETERMINATION 



85 



dish. If no chlorid of lime is contained in the original soil be- 
fore the evaporation takes place a half gram of calcium carbonate 
is added to the solution. The residue from drying is heated care- 
fully and in order to avoid too rapid evaporation a platinum or 
nickel plate is placed between the source of the heat and the 
dish. After complete dryness has been secured, the flame is so 
regulated that the bottom of the dish containing the residue is 
heated almost to a low red heat, but even in this case the volatili- 
zation of the aluminium chlorid is not to be feared. After the 
vigorous evaporation of the vapors of hydrochloric acid has 
diminished somewhat the platinum or nickel plate is laid upon 
the top of the dish. The mass within the dish soon reaches a 
condition in which it can be rubbed into a fine powder by a glass 
rod, after which it is heated a while longer and stirred contin- 
ually until all parts of the material are reduced to a fine pow- 
der. After about an hour of treatment of this kind the organic 
substances which the solution may contain are completely de- 
stroyed and the residue is ready for further investigation. 

The contents of the dish are washed in a 125 cubic centimeter 
flask with a sufficient quantity of water to fill the flask half full 
and the contents of the flask are boiled over a low flame for about 
half an hour; after cooling, the flask is filled to the mark, thor- 
oughly mixed and filtered through a very small dry filter into a 
dry vessel. The filtrate must be completely colorless and at most 
only slightly alkaline, and if the operation above indicated has 
been properly carried out, it is entirely free from iron, phosphoric 
acid and silicic acid. One hundred cubic centimeters of the fil- 
trate, corresponding to 20 grams of the original soil, is the quan- 
tity used, if the volume of insoluble material is not taken into 
consideration. 

If a correction is desired for this, the ignited residue is weighed 
and its volume approximately calculated by taking into consid- 
eration its specific gravity and weight. 

In a porcelain dish 100 cubic centimeters of filtrate are evap- 
orated to dryness, a few drops of hydrochloric acid added and a 
sufficient quantity of platinum chlorid for the determination of 
potassium salts in the usual manner. Inasmuch as other salts 



n,ay be found in this operation, their separat.on . recommended 

by the method described ^Y Neu^--^ .^^^^,^ ^^,,,,,, 

For the estimation of ^^J °^^^/^^^^^^^^^^ is used. 

irtthis: ::ztz:'^:^^ro.^ . sm., .te. .pc^n 

,1 the reddish brown precipitate has been collected, rep ac. 

"'r rjS::;™r J srj."» (SOU) .hic, .,as.,ee,, 

:ratd anXc n,l"n.ly *..™i™„ b, ll,» n,„,ybda,. ,™,ho _ 

Tl , tol b<la« m«l,o,l i. r«c«,m,e„.lcd bee.,.,., even w, b a 1 

Tcarc vhicb ha, b„„ exercke.l. the ,ob,lion .„u.ll, ,t.ll con- 

Tl He ahcvhc ackl. No.baner, however, h.ghl, recom- 

r-,', t^, ct:: f^r ,he .,.,.».„„ o. ^-^^-^^jx 

rest of the process is carried out as describe.! 

"'"'"'the e,ti.,„tio„ ot calcium and masnesi.,,. »»"'" P"'™; 

r e deser.h.,, -.^^^ -^ -^ Z:^t7i:i^^ 
cuim carbonate. 1 he resume ib otlierwise it is evident 

should eive no trace of an acul reaction. Otherwise it is ev 
tt 1 deposition of the chlorid has not been sufficiently se- 

"According to the estimated quantity of calcium from about two 
» Zeilschrift fur analytUche Chetnie. 1904, 43: 14. 



li 



86 



AGRICULTURAI. ANAI.YSIS 



to five grams of ammonium chlorid are added and the mixture 
heated upon the water bath until no further evaporation of am- 
monia takes place. The mixture is washed in a 125 cubic centi- 
meter flask and treated with a few drops of ammonia, boiled a 
few minutes, cooled, filled to the mark, filtered through a small 
dry filter and 100 cubic centimeters of the filtrate, corresponding 
to 20 grams of the soil, used for the estimation of lime and 
magnesium by the usual methods. 

Neubauer claims that the method described is recommended 
particularly by reason of its speediness. According to him, it 
also has other advantages. For instance, the precipitation by 
ammonia and ammonium carbonate is avoided in which a slimy, 
difficultly filterable precipitate is often produced which can easily 
intertangle notable quantities of phosphoric acid and potash. The 
filtrate from the iron and aluminium precipitate must, on account 
of its ammonia and ammonium carbonate, be very carefully evap- 
orated to dryness in order to avoid loss by spurting. 

Finally, one of the especial advantages of the process appears 
to be that the disturbing influences of organic substances is com- 
pletely eliminated and no impure potassium platinum chlorid or 
brown cojored phosphoric acid precipitate is any longer possible. 

This method, which is originally designed for application to 
soils, may be used, apparently, with advantage in the examination 
of slags containing small quantities of potash and phosphoric 
acid to determine their value as fertilizing material. A quantity 
ot phosphoric acid and potash, especially the latter, which is 
directly soluble in hydrochloric acid, may prove to be an index 
of the comparative availability of these two plant foods contained 
in slag. 

87. The Color of the Magnesium Pyrophosphate.— After the final 
Ignition of the magnesium pyrophosphate, whether secured by 
the citrate or the molybdate method, a black or grayish tint is 
often noticed. This may be due to traces of organic matter 
brought down by the precipitate and especially to a lack of care 
m the initial ignition. Many devices have been ])roposed for 
the purpose of avoiding this coloration, although general experi- 



DETERMINATION OF PHOSPHORIC ACID AND NITROGEN 87 

ments have shown that there is no appreciable increase in the 
weight of the precipitate when colored in this way. 

When the precipitation is carried on according to the citrate 
method, Neubauer proposes to eliminate this coloration by the 
use of ammonium sulfate.^^ About seven cubic centimeters of a 
saturated solution of ammonium sulfate should be added to the 
solution before the precipitation by the magnesium mixture. 
With this precaution it is possible to obtain a perfectly white 
precipitate after five minutes of ignition. The lively glowing of 
the precipitate throughout the whole mass at the time of changing 
into pyrophosphate is much more easily observed by this treat- 
ment than when the mass is gray or black. Even should the 
addition of the ammonium sulfate solution to one containing a 
large amount of lime produce a precipitate of crystalline calcium 
sulfate, it is of no importance, inasmuch as the ammonium citrate 
immediately dissolves large quantities of the calcium salt. 

A white pyrophosphate is easily obtained by treating the pre- 
cipitate on the gooch after washing free from chlorids with a drop 
or two of ammonium nitrate. The ignition is commenced very 
gently at first and afterwards, when the mass is white, the blast 

is used. 

If the ignited residue be gray it may sometimes be wdiitened by 
moistening with a drop or two of nitric acid, burning at a very 
low temperature, followed by the blast. There is no appreciable 
difference in weight between a gray and white pyrophosphate. 

88. Determination of Phosphoric Acid and Nitrogen in the Same 
Solution by Treatment with Sulfuric Acid and Mercury.— Fertiliz- 
ing materials which contain organic nitrogen and phosphoric acid, 
such as bones, are of such a nature that it is often difficult to ob- 
tain a fair sample of them in quantities suited to the direct deter- 
mination ; viz., about one gram. Thus it often becomes important 
to take a much larger quantity of the material, to bring it into 
solution and to take an aliquot part thereof. It may also often 
happen that it is important to determine the phosphoric acid in 
the same sample which has been used for the determination of 
the nitrogen by moist combustion with sulfuric acid and mercury. 
^» Zeitscbrifl fiir angewandte Chemie, 1894, 7 : 678. 



' I 



1 r 






I 



i 



88 



AGRICUI^TURAL ANALYSIS 



GENERAL PRINCIPLES 



89 



In this connection, however, it is somewhat difficult to avoid the 
precipitation of some of the mercury with the phosphoric acid 

The mercuric sulfate which is produced by the Kjeldahl method 
IS not precipitated in the presence of ammoniacal solution of am- 
monuim citrate, but there may be small quantities of mercurous 
salts present or some finely divided metallic mercury which may 
contaminate mechanically the phosphate precipitate. These dis- 
turbing inOucnces may be removed by previous treatment with 
sodium chlorid. If from 50 to 60 cubic centimeters of sul- 
furic acid have been used for the solution and oxidation and this 
be made up to .half a liter, it will be sufficientlv dilute to permit 
an almost quantitative separation of the mercurous chlorid pro- 
duced by treatment with sodium chlorid. 

Neubaucr. who has proposed this method, finds that when 
sodium chlond is used previous to the precipitation of the phos- 
phoric acid, a precipitate of ordinary size contains, at most, only 
one milligram of mercury, while without the use of sodium chlorid 
as much as four milligrams may be found. The details of the 
method employed by Neubauer are as follows •'"' 

Ten grams of the fertilizing material are placed in a half liter 
flask with from 50 to Tx, cubic centimeters of strong sulfuric 
acid, two grams of mercury, and a little paraffin to prevent foam- 
ing. The oxidation is carried on as usual in the Kjeldahl method 
T he liquid, after cooling, is diluted with water and one cub^c 
centimeter of a citrate solution of sodium chlorid added, cooled 
filled to the mark, filtered, an<l 50 cubic centimeters taken fo^ 
Uie determination of the phosphoric aci.l, according to the citrate 
method and the same quantity for the determination of the am- 
monia by distillation. The methods of digestion of soils with 
u unc aci,l described in Volume I, are also applicable t; 
lertilizing materials. 

THE CITRATE METHOD 
89 General Principles.-lt has been seen that in the molvbdate 
n ethod there is introduced a process at considerable cost botb 
o reagents and time, having for its object the separation ;f t 
Pliosphonc acid from all the other acids and bases which may 

Zeitschrift fur angewandte Cheniie, 1894, 7 :678. 



have been present in the original sample. The phosphorus is thus 
obtained in composition with molybdenum and ammonium in a 
form easily soluble in ammonia, from which it can be accurately 
separated by means of a sokible salt of magnesia. 

The citrate method has for its object the suppression of this in- 
termediate step and the determination of the phosphoric acid by 
direct precipitation in presence of iron, lime, and alumina. The 
principle in which it is based rests on the well known power of 
an alkaHne ammonium citrate to hold in solution the salts of iron, 
alumina, and lime, while at the same time it permits of the separa- 
tion of phosphoric acid, as ammonium magnesium phosphate. In 
no case can the citrate method be regarded as a rigidly exact an- 
alytical process, but large experience has shown that the errors 
of the method are compensatory and that it affords a good and 
ready method for fertilizer control. 

When phosphoric acid solutions which contain no iron, lime, 
alumina, or manganese, are precipitated in presence of ammonium 
citrate the results obtained vary markedly with the quantity of 
magnesia mixture employed. Grupe and Tolllens were the first 
to point out that a portion of the phosphoric acid might remain 
in solution, but that the precipitate might contain a sufficient 
excess of magnesia to compensate for the loss.^^ If lime, iron and 
alumina, moreover, are present, the precipitate obtained is not 
wholly free from these bodies. It is true that the quantities of 
these bodies found in the precipitate are quite small, but they may 
at times influence the accuracy of the results. The presence of 
lime and magnesia in the precipitate, as already mentioned, is 
indicated by the yellow color produced by moistening the white 
ignited precipitate with silver nitrate.'^ It has been further shown 
by Glaser, as well as by Neubauer, that a portion of the phos- 
phoric acid may be lost by volatilization in the citrate method.®'^ 
When the ignition is carried on in a crucible where the cover is 
coated with magnesia to intercept the volatilized acid, a considera- 
ble quantity of it can be recovered by the molybdate method. 

«i Journal fiir Landwirtschaft, 1882, 30 : 23. 

«^ Tolleus, Journal fiir Landwirtschaft, 1882, 30 : 48. 

«3 Zcitschrift fiir angewandte Chemie, 1894, 7 : 544- 



HI 



90 



AGRICULTURAI^ ANALYSIS 



Where too little magnesia mixture is employed, therefore, two 
sources of loss are to be guarded against ; viz., a part of the 
phosphoric acid may remain in solution and another part be vol- 
atilized on ignition. The explanation of the volatilization is as 
follows : In the presence of ammonium citrate, magnesium chlorid 
may be partly converted into magnesium citrate and ammonium 
chlorid. There may be a time, therefore, in the precipitation 
with not too great excess of magnesia mixture, when propor- 
tionally there is little magnesium chlorid and much ammonium 
chlorid present. The formation of a salt represented by the 
formula 2Mg(NH4),(P04)o may take place which, upon ignition, 
breaks up into 2Mg(P03)2 and finally passes into Mg^PoO^ with 
loss of P0O5. This theoretical condition has but little weight, 
however, practically in the analysis of fertilizers, since in these 
cases a large quantity of lime is always present. But even in 
these cases traces of volatile P0O5 may be discovered. 

Wells has shown that the citrate method gives good results 
in certain conditions, but that this accuracy is reached by a for- 
tunate compensation of errors.^* The ammonium magnesium salt 
does not precipitate all the phosphoric acid in this process, but 
contains enough impurities to make up for this loss. 

Johnson in conjunction with Osborne has shown that the re- 
sults by the citrate method practiced in accordance with the details 
laid down by \^ogel, are too low, but that this difficulty could be 
overcome by using more and stronger magnesia mixture and a 
larger quantity of strong ammonia solution.^* The citrate method 
was found to give unsatisfactory results when iron and alumina 
were present in any considerable quantity, in the examination of 
the final ignited precipitate, which should be pure magnesium 
pyrophosphate, it was found to consist of only from 94.98 to 97.83 
per cent, of that salt. The chief impurity found was calcium oxid, 
the percentage of which varied from 2.05 to 3.95 in six cases.' 
There was also a considerable percentage of loss due, probably, 
to magnesia and pyrophosphoric acid. 

The presence of large quantities of iron and alumina also im- 
pairs the accuracy of the molybdate method when the precipita- 
«♦ Journal of the American Chemical Society, 1894, 16 : 462. 



METHOD OF HALLE EXPERIMENT STATION 



91 



tion of the yellow salt takes place at too high a temperature. When 
the temperature of precipitation in the method is above 50 the 
results are likely to be too high, while a great excess of nitnc 
acid in the reagent may produce a contrary effect. In the lattei 
case the filtrate from the yellow salt should be mixed with addi- 
tional quantities of molybdate solution until no further precipitate 

takes place. 

Many methods of conducting the citrate method have been pro- 
posed but the best of them are based on the one elaborated at 
the experiment station of Halle by Biihring, and which will be 
given in the next paragraph, followed by some other methods m 
use in other localities. 

90. Method of Halle Agricultural Experiment Station.^^— 
The citrate method elaborated by Biihring, as described by Mor- 
gen, is the one employed.«« The principle depends upon the direct 
precipitation of the phosphoric acid by magnesia mixture. By 
the addition of a solution of ammonium citrate the precipitation 
of lime, iron, alumina and other bases is practically prevented. 
The precipitate of ammonium magnesium phosphate is converted 
by ignition into magnesium pyrophosphate and weighed as such. 
By the use of this method a part of the phosphoric acid some- 
times escapes precipitation and a portion of the other bases is 
sometimes thrown down with the precipitate. Experience has 
shown that bv adhering to certain precautions the weight of im- 
purities in the precipitate may be made to correspond very nearly 
to the weight of the phosphoric acid which escapes precipitation. 
(I) Soluble Acid.— The soluble phosphates are first brought 
into solution in such a way that one liter of water contains the 
soluble phosphoric acid from 20 grams of the substance. 
Twenty grams are rubbed in a porcelain mortar with water and 
through a wide-necked funnel washed into a bottle-shaped flask 
in which a little water has been previously placed. The flasks em- 
ployed are made of thick glass in order to withstand shaking. 
After the substance is washed in, the flasks are filled to the mark 

«^ Bieler iind Schneidewind, Die agrikultiir-chemische Versuchsstation, 
Halle a/S, ihre Einrichtung undThatigkeit, 1892 : 56. 
6« Die cheniische Industrie, 1890, 13 : I35i I39- 



=1 



92 



AGRICULTURAL ANALYSIS 



and closed with rubber stoppers. They are placed upon a shaking 
rack, as indicated in Fig. 3, which is also furnished with an ap- 
paratus for separating the fine meal from the basic slag. 

On a table, as shown in the figure, is fastened a movable hori- 
zontal board by means of hinges. On one side of this movable 
board is placed an open wooden box in which is a perforated 
shelf for the purpose of holding the flasks, so as to prevent their 
striking together during the shaking. On the other side is placed 
the sifting apparatus above mentioned. The to and fro move- 
ment of the shaker is imparted by any convenient mechanism. 

Good results are obtained by placing the substance to be exam- 




Fig. 3. .Shaking Apparatu,s for Superphosphates. 



ined in the flask in a dry state, adding cSoo cubic centimeters of 
water and shaking by means of the machine indicated for half 
an hour. Afterwards the flasks are filled up to the mark, well 
shaken and their contents filtered through double folded filters into 
ordinary flasks of about 400 cubic centimeters capacity. Before any 
of the filtrate is collected the first that runs through should be 
well shaken in the receiving flasks and rejected. Fifty cubic centi- 
meters of the filtrate thus collected, corresponding to one gram 
of the substance, should be used for the determination. 

(2) Total Acid.— Vor total pho.sphoric acid, including the in- 
soluble portions, except in the case of basic slags, the material is 
treated as follows : Five grams of the substance are placed in a 



METHOD OF HALLE EXPERIMENT STATION 



93 



,00 cubic centimeter flask with 20 cubic centimeters of nitric 
'cid of .42 specific gravity, and 50 cubic centu.eters of pure 
Concentrated sulfuric acid, and boUed briskly for ^U an hour^ 
With substances which contain much organic material, a little 
paraffin is added to avoid frothing. Such substances also require 
a larger quantitv of nitric acid than that above specified. The 
flasks are allowed to cool, water added, again allowed to cool 
and filled up to the mark at I7^5■ " hydrochloric instead o 
sulfuric acid be used in making the above solution, when he 
citrate method is employed, the results are always too h^h be- 
cause the precipitate contains lime and alumina m such quantities 
as to render anv compensation for them inaccurate. In addition 
to this the sulfuric has this great advantage over the hydro- 
chloric acid ; VIZ.. it does not separate the silicic acid, inasmuch 
as silicic acid is insoluble in boiling sulfuric acid. 

(.) Citrate-Soluble Acid.-As is well known, in acidulated 
phosphate a part of the phosphoric acid at first soluble in water 
becomes insoluble, or, as usually expressed, reverted^ ^}'''^Z' 
tion, however, is still .uluble in ammonium citrate. By the Hale 
method it is determined as follows : Two grams of the sample 
are digested with 100 cubic centimeters of ammonium citrate so- 
lution, 1.09 specific gravity, for half an hour at 50° in a beaken 
Afterwards the soluble matter is separated by filtration with the 
aid of a filter-pump and the residue washed with a solution of one 
part water and one part citrate solution until all the dissolved 
phosphoric acid is removed from the filter. Generally three or 
four washings are sufficient. The residue on the filter is dried 
icnited and dissolved in a mixture of two cubic centimeters of 
nitric and 20 cubic centimeters of sulfuric acid, the solution 
made up to a volume of 200 cubic centimeters, filtered, and 100 
cubic centimeters of the filtrate used for the determination. The 
acid in the filtrate is nearly neutralized and 50 cubic centimeters 
of the citrate solution used in the determination of total acid are 
added, and afterwards 25 cubic centimeters of magnesia mix- 
ture and 20 cubic centimeters of 24 per cent, ammonia. After 
standing for 48 hours, the precipitate is separated by filtration, 
icrnited, and weighed in the usual way. The difference be- 



H 



r 4'| 



94 



AGRICULTURAL ANALYSIS 



METHOD OP HALLE EXPERIMENT STATION 



95 



1 



tween the total phosi^horic acid and that in the insoluble residue, 
after treatment with ammonium citrate, as above, gives the' 
quantity of phosi^horic acid soluble in citrate solution. The 
difference between the total citrate-soluble and the water-soluble 
gives the quantity of the reverted phosphoric acid. 

The ammonium citrate solution (Petermann's) used for the di- 
gestion is made as follows : Two hundred and fifty grams of crys- 
tallized citric is dissolved in half a liter of hot water, diluted 
with 550 cubic centimeters of water, 276 cubic centimeters of 
24 per cent, ammonia added, and finally, exactly neutralized by 
addmg, little bV little, 50 per cent, citric acid solution. 

The Halle methods of separating the water and citrate-soluble 
acids appear to be less complete and reliable than those in use 
by the Official Agricultural Chemists of this country. The pre- 
cipitation of basic phosphates, when large quantities of water are 
used at once in separating soluble acid, must tend to diminish 
the quantity obtained, while the lack of care in assuring the neu- 
trality of the citrate solution might lead to varying results. 

(4) Double Supcrf>hosphatcs.~ln the case of double super- 
phosphates, which sometimes contain large quantities of pyro- 
phosphate, the solution is made in the usual way so that in 100 
cubic centimeters there will be contained two grams of the sub- 
stance. Usually 10 grams are used and the volume made up 
to half a liter. Twenty-five cubic centimeters of the filtrate are 
diluted with 75 cubic centimeters of water and the pvro- 
converted to orthophosphoric acid by heating with 10 cubic ceiui- 
meters of strong nitric acid on a sand-bath. The heating should 
be continucl until the volume is reduced to 25 cubic centimeters 
The strongly acid lic|uid is made alkaline with ammonia and after- 
wards slightly acid with nitric acid, and the rest of the process 
is carried on in the usual way. 

(5) Phosphoric Acid in the Residue of Superphosphate Manu- 
facture-In the mixture of superphosphates and gypsum, the res- 
idue of the manufacture of double superphosphates, the phos- 
phoric acid is estimate.! in the following manner : Five grams 
of the substance are placed in a dish, rubbed up with absolute al- 
cohol, and washed into a 250 cubic centimeter flask. The flask is 



■CI. 



filled with absolute alcohol to the mark, closed with a stopper, 
and, with frequent shaking, allowed to stand for two hours ; it is 
thereupon filtered as quickly as possible ; 50 cubic centimeters of 
the filtrate, corresponding to one gram of the substance, is used 
for the estimation. This is evaporated on a sand-bath to a sirupy 
consistence, diluted with water and treated as in the case oi the 
soluble phosphates above mentioned. In all cases, as described 
above, after the solutions are obtained they are treated with the 
ammonium citrate solution and the phosphoric acid estimated as 
in the method for soluble acid. 
(6) Solutions Employed. — 

(a) The citrate solution is made as follows: Fifteen hundred 
grams of citric acid are dissolved in water, treated with five 
liters of 24 per cent, ammonia, and made up to 15 liters. 

(b) The magnesia mixture is made as follows: Five hundred 
grams of magnesium chlorid, 1050 grams of ammonium chlorid, 
thrqe and five-tenths liters of 24 per cent, ammonia, and six and 
five-tenths liters of distilled water are used. 

In the case of the superphosphates 50 cubic centimeters of 
the citrate solution are employed and with the basic slags 100 
•cubic centimeters ; and in both cases 25 cubic centimeters of the 
magnesia mixture. 

(7) Details of the Manipulation.— On the addition of the citrate 
solution there should be no permanent troubling of the liquid, but 
any precipitate at first formed should entirely disappear after the 
addition of the whole quantity of the reagent, in order to facili- 
tate this, after the addition of the citrate solution the flasks should 
be gently shaken so as to distribute the solution throughout 
the mass. Solutions from bone-black superphosphates show 
sometimes, after the addition of the citrate solution, a more or 
less strong opalescence, but this opalescence does not influence 
the results. Should it happen that with superphospbates which 
are made from raw material containing large excesses of iron or 
clay 50 cubic centimeters of the citrate solution are not suffi- 
cient to prevent the other bases from being precipitated, an addi- 
tional quantity uj) to 25 cubic centimeters may be added. 
The addition of the magnesia mixture must follow as quickly as 



51 

^1 



I .*1 



JM 



96 



AGRICULTURAL, ANALYSIS 



METHOD OF HALLE EXPERIMENT STATION 



97 



possible after the addition of the citrate sokition to avoid a sep- 
aration of crystalhne calcium phosphate. On the addition of the 
citrate solution there is always a rise in temperature. Inasmuch 
as the precipitation of the phosphoric acid with magnesia must 
take place in the cold, the liquid must be cooled after the addi- 
tion of the citrate, and the cooling should take place as quickly 
as possible. 

The above method was adopted by the chemical section of the 
International Agricultural Congress held at Vienna, September. 

In order to hasten the precipitation of the ammonium magne- 
sium phosphate and to prevent the fixation of the precipitate on 
the walls of the erlenmeyer, the flask should be shaken for half 

"" rZ- u^'' ''"'■P°'' ^^^ ^""'^^ ''^°"'^' ^' c'o-^ed with smooth 

well-fitting rubber stoppers and placed in a shaking machine. The 
shaking machme of the form given in Fig. 4, recommended by 
the Halle station, is very conveniently used for this purpose. 

r 







TMl||!i,|);!i;|ll|'iir,Tinin 



Fig. 4. Shakmg Machine for Ammonium Magnesinn. Pho.sphate. 



^-^ •" ^'■"ijiicr.uiin I'no.spnate. 

fh?k^ ' tT'"^' T" ''' '"""^ '"" P^^^^"^"^^ ^^^ holding the 
flasks. The flasks are prevented from striking each other hy 

dZ: b T''"" ^''""- ^^^^ ^^^^^^^- ^^ conveniently' 

c^ ven by a small water-motor, as indicated, which imparts to th' 
platforms a partial back and forth revolution * 

After shaking for half an hour, any precipitate adhering to the 
ubber stoppers . carefully washed off with ammonia water into 
the flask The filtration can be made immediately after the shak- 
ing or after two or three days; the results are the same. 

•^ Chemiker-Zeituiig, 1890, 14:1246. 



The filtration of the ammonium magnesium phosphate is made 
through gooches. The asbestos felt is prepared in the following 
way : The coarse fibers of asbestos are chopped up with a sharp 
knife on a glass plate and boiled for two hours with strong hydro- 
chloric acid ; afterwards, by repeated washing with distilled water, 




Fig. 5. Rossler Ignition Furnace. 

they are freed from acid and the fine particles of asbestos which 
w^ould tend to make the filter too impervious. After the last wash- 
water is poured off, the asbestos is suspended in water and used 
for making the felt on the filter. The preparation of the crucible 
and the filtration under pressure are accomplished in the usual 
way. 

The ignition of the precipitate is accomplished in a Rossler ig- 



li 



98 



AGRICIJI.TURAL ANAI.YSIS 



METHODS ADOPTED BY THE BRUSSEI.S CONGRESS 99 



riition oven, Fig. 5. When the muffle of the furnace shows a 
white heat or a white-red heat, it is at the proper temperature for 
the estimation. At higher temperatures, the filtering property 
of the asbestos felt is easily injured. Generally, an ignition of five 
minutes is sufficient, but with double superphosphates, 10 min- 
utes are required. 

91. The Swedish Citrate Method.^^— This method of determina- 
tion is a modification of the citrate method already described and 
is founded on the observation that phosphoric acid in the pres- 
ence of calcium salts, without the necessity of previously con- 
verting into phosphomolybdate, is precipitated directly by mag- 
nesia mixture from a solution to which ammonium citrate has 
been added, provided first, that the solution contain a sufficient 
quantity of sulfuric acid to convert all the calcium compounds 
into sulfates, and second, that only as much citrate be added as 
is required to keep the calcium salts in alkaline solution. In other 
words, it IS the method of separation devised by C. Glaser and 
others.^® 

Reagents, (i) Citric Acid Solution. — Prepared by dissolving 
500 grams of citric acid in water and completing to a volume of 
one liter. 

(2) Ammonia of 0.959 specific gravity. 

(3) Magnesia Mixture, composed of 140 grams of magnesium 
sulfate, 150 grams ammonium sulfate, and 30 grams of chlorid of 
ammonium dissolved in 350 cubic centimeters of 16 per cent, am- 
monia and 1650 cubic centimeters of water. The ammonium 
chlorid is added to prevent the precipitation of basic magnesium 
sulfate. 

The various processes are conducted as follows : 
(a) Water-Soluhle Phosphoric Acid.— AM 20 cubic centi- 
meters of citric acid solution to 50 cubic centimeters of the 
water-soluble solution obtained according to the Swedish molyb- 
date method, and then add 33 cubic centimeters of ammonia. 

•'^ Official Swedish Methods Translated for the Author by F. W. Well. 
«» Zeitschrift fiir analytische Chemie. 1885, 24 : 178; 1886, 25 : 416. 

Chemiker-Zeitung, 1888, 12 : 85, 492. 

Zeitschrift fiir angewaiidte Chemie, 1888, 1 :354. 

Die landwirtschaftlicheii Versuchs-Stationen, 1888, 35 1439. 



When the mixture has cooled, add slowly 25 cubic centimeters 
of the magnesia mixture, and then 42 cubic centimeters of the 
ammonia. Keep the solution stirred by means of a closely 
clipped feather which is pressed tightly against the sides of the 
beaker; by this process the phosphate is precipitated after half 
an hour in pure condition and completely without in the least 
•sticking to the wall of the beaker; filter, wash, and ignite, as 
usually directed. 

{h) Insoluble Phosphoric .4 a J.— Moisten, in a porcelain dish, 
10 grams of the powdered sample with water; add 50 cubic 
centimeters of concentrated sulfuric acid, and heat for 15 min- 
utes so that fumes of sulfuric acid will escape. When the mass 
has cooled, wash it into a half-liter graduated flask, fill to 
the mark, and shake well. After filtration, the clear filtrate may, 
after some time, turn turbid by separation of calcium sulfate, but 
as the ammonium citrate, which is afterwards added, again brings 
the precipitate into solution, it is of no importance. Add to 50 
cubic centimeters of the solution, corresponding to one gram of 
the powdered sample, 20 cubic centimeters of the citric acid 
solution, neutralize the mixture approximately, but not exactly, 
by ammonia ; after cooling, add 25 cubic centimeters of magnesia 
mixture; stir the fluid by means of a feather, as described, till- 
no more precipitate is formed, and finally add 33 cubic centi- 
meters of ammonia while stirring for several minutes longer; 
after half an hour the precipitate may be separated by filtration, 
washed, and ignited, as usually directed. 

The above process is essentially the one used with basic slags. 
When much organic matter is present, by continuing the heating 
with sulfuric acid for some time it may be destroyed. 

92. Methods Adopted by the Brussels Congress, 1894.— The re- 
port of the committee on methods of analysis of phosphoric acid 
requires the molybdate method to be used in all cases where the 
quantity to be determined is very small. In other cases the citrate 
method may be employed.'^^ 

(i) Soluble Phosphoric ^cu/.— The soluble phosphoric acid is 
determined by the method adopted at Brussels in the following 



ill 



m 
in 



:i 



70 



L'Engrais, 1894, 9 : 928. 



lOO 



AGRICULTURAL ANALYSIS 



METHOD OF LASNE 



lOI 



manner : Five grams of the sample are rubbed to a powder in a 
mortar, and then from 50 to 60 cubic centimeters of water 
added. After allowing to settle for a few minutes the liquid por- 
tion is decanted upon a filter. This operation is repeated three or 
four times. Finally, the solid portions are washed upon the filter, 
and the washing with water is continued until the filtrate amounts 
to about three-quarters of a liter. A few drops of hydrochloric 
acid are added until the filtrate is perfectly clear, and the volume 
is then made up to one liter. Fifty cubic centimeters of the solu- 
tion are then treated with 30 cubic centimeters of ammonium 
citrate solution and one-third as much ammonia. Afterwards 
30 cubic centimeters of magnesia mixture are added, drop by 
drop, with constant stirring. 

For superphosphates containing more than 18 per cent, 
of phosphoric acid only one gram of the sample is used, for ordi- 
nary superphosphates two grams, and for compound fertilizers 
four grams. The sample is first treated as above for soluble acid 
until the filtrate amounts to 200 cubic centimeters, then clarified 
with a drop of nitric acid, and made up to a quarter of a liter. 

(2) Reverted Phosphoric Acid. — The filter containing the resi- 
due is then introduced into a quarter liter flask and treated with 
100 cubic centimeters of Petermann's alkaline ammonium citrate 
solution, vigorously shaken, and left at room temperature for 
15 hours. It is digested for an hour at 40° and filtered. Fifty 
cubic centimeters of the filtrate are placed in a flask and, with 
constant shaking, 35 cubic centimeters of magnesia mixture added. 
The aqueous solution is treated in the same way. The precipi- 
tate is collected, washed with two and one-half per cent, ammonia 
until the chlorin disappears, ignited, weighed, and the number 
obtained multiplied by 0.64 for phosphoric acid. The total acid is 
determined in the usual way. 

93. Dutch Method for Citrate-Soluble Phosphoric Acid.— The 
reagents necessary are : 

(i) Citrate solution. Dissolve 165 grams of citric acid in 
700 cubic centimeters of water, mix with 250 cubic centimeters 
of ammonia of 0.92 specific gravity, and, aft r co ling, bring to 
the volume of one liter. 



(2) Magnesia mixture. Dissolve 400 grams of crystallized 
magnesium chlorid, 800 grams of ammonium chlorid, and 1600 
cubic centimeters of ammonia of 0.96 specific gravity in water, 
and dilute to five liters. 

The quantity used for the analysis is five grams where the fer- 
tilizer contains less than six per cent, of phosphoric acid (mixed 
fertilizers) ; two grams where it contains more than six and less 
than 15 per cent, (common superphosphates); and one gram 
where it contains more than 15 per cent, (double superphos- 
phates). Place the weighed substance in a mortar and cover 
with 100 cubic centimeters of citrate solution. Gently rub up, 
wash into a half liter flask, and heat on a water bath for an hour 
to a temperature between 35° and 38^ Allow to cool, fill up to 
500 cubic centimeters, and filter through a dry double filter. If 
the liquid is not clear at the first titration, i^ur through the filter 
again, repeating this till clearness is attained. To 100 cubic centi- 
nteters of the filtrate add 75 cubic centimeters of magnesia mix- 
ture, allowmg the latter to flow into the former very slowly, and 
constantly stirring during the influx. Allow to .stand 15 hours, 
filter, wash with ammonia of 0.96 specific gravity, dry, ignite, and 

weigh. 

The per cent, of phosphoric acid, except where otherwise indi- 
cated, is always to be given as per cent, of phosphorus pentoxid 

(P2O.). 
94. Method of Lasne.— Lasne recalls some previous observations 

which are confirmed by later ones, as follows :'^ 

(i) The precipitation of ammonio-magnesium phosphate takes 

place without loss when conducted in the presence of citrate of 

ammonia, and with a sufficient excess of magnesia. 

(2) Lime, oxid of iron, alumina and manganese are carried 
down by the precipitate. 

(3) The presence of silica and of fluo-silicates causes an excess 
of weight in the precipitate over the probable amount due to phos- 
phorus. 

(4) Without the addition of an excess of magnesia the precipi- 

71 Bulletin de la Social chimique de Paris, 1897, [3], 17:82.3 and 
following. 



■cl 



w 



4 



I02 



AGRICULTURAL ANALYSIS 



tation is incomplete and the separated liquid is precipitated alike 
b\ magnesia and phosphoric acid. 

The results of the work show that when stirred with ammonio- 
magnesium phosphate the final result is obtained without any loss, 
and that on calcination the identical weight with which the experi- 
ment commenced is obtained. The conclusions obtained by Lasne 
from a large mass of analytical data are summarized as follows : 

( 1 ) The formation of phosphoric acid in the state of pyrophos- 
phate without any other precaution than previous elimination of 
silica gives results which are not affected by any systematic error. 

(2) Rapid precipitations cause an excess of weight in the pre- 
cipitate due to a partial formation of tri-magnesium phosphate, 
which is only transformed into ammonio-magnesium phosphate by 
contact for 16 hours with a sufficiently concentrated solution 
of ammonium citrate, namely, containing ten grams of citric acid 
in 150 cubic centimeters of the solution. It is necessary, there- 
fore, in order to obtain rigorous results, to allow the precipitate 
to stand before filtering for at least 16 hours. Nevertheless, it 
must be admitted that this excess of weight is so small as not to 
warrant the complete rejection of the rapid methods for all in- 
dustrial purposes when proper precautions are employed. 

(3) The transformation of tri-magnesium phosphate into am- 
monio-magnesium phosphate takes place very slowly in the pres- 
ence of ammonium chlorid alone, and there should always, there- 
fore, in these precipitations, be added the quantity of citrate of 
ammonia indicated above. 

The precipitation of magnesia in the presence of an excess of 
ammoniacal phosphate gives, in addition to ammonio-magnesium 
phosphate, a phosphate poorer in magnesium, and as much poorer 
as the excess of phosphoric acid is larger. The determination of 
magnesia by this classical method is always erroneous. 

95. Comparative Accuracy of the Citrate and Molybdate Metii- 
ods. — The general use of the citrate method of determining phos- 
phoric acid by the German chemists has led Johnson to review 
some trials of that method in his laboratory made as early as 
1880.^- These determinations have lately been repeated in com- 

^' Journal of the American Chemical Society, 1894, 16 : 462. 



S 



CITRATE AND MOLYBDATB METHODS 



103 



parison with the ordinary molybdate methods, with the result 
that in 67 determinations on bone-dust, superphosphate, 
cotton-hull ashes, cottonseed-meal, tankage, bone-char, phosphatic 
guano, and phosphate rock, only three citrate results differed from 
those obtained by the molybdate method by more than three- 
tenths of one per cent. The greatest discrepancy between the two 
methods was 0.41 per cent., and the average difference was 0.09 

per cent. 

Attention has already been called to the fact that the citrate 
method was found to give poor results when iron and alumina 
were present in considerable quantity. Ignited precipitates by the 
citrate method were found to contain as high as four per cent, of 
lime, and iron and alumina in small quantities when these bodies 
were abundant in the original substance. 

In the molybdate method the rapid precipitation from solutions 
at 65° was found to give unsatisfactory results and it was found 
necessary to conduct the process at temperatures between 40° and 
50°. With a relative excess of nitric or a relative deficiency of 
molybdic acid some phosphoric acid may easily escape precipita- 
tion. The chief objection to precipitating at 65^ is found in the 
fact that in presence of considerable iron and alumina some of 
these bodies may be found in the yellow precipitate, whence they 
pass to the final ammonium magnesium phosphate. 

The citrate method, therefore, only gives safe results by com- 
pensating errors which in every class of phosphates must be em- 
pirically determined. 

The molybdate method gives results too high when iron and 
alumina are present in considerable quantity and the yellow pre- 
cipitate is obtained at temperatures above 50°. On the other hand, 
if there be a great relative excess of nitric acid the results may 
be too low unless the filtrates from the yellow precipitate be mixed 
with additional molybdic solution and digested until no further 
precipitate is formed. 

Comparative determinations made by both methods by Maercker 
for the Association of German Exi)eriment Stations have led to 
the conclusion that both give practically the same results wdien 



1^1 
m 






THE CITRATE METHOD 



^05 



104 



ACRICUIvTURAJ. ANALYSIS 



each one is conducted with the proper precautions pecuHar to it.'^^ 
in the latter part of 1892, at the general meeting of the associa- 
tion, it was declared that the citrate method, after having been 
subjected to repeated tests, was found to be satisfactory, changing 
the composition of the solution so that it might have iioo instead 
of TOGO grams of citric acid and four liters of 24 per 
cent, ammonia to each 10 liters. The data afforded by the citrate 
method, when applied to an artificial mixture of known composi- 
tion, were more satisfactory than those obtained by the molyb- 
dic process. 

In the laboratory of the Bureau of Chemistry the citrate method 
has been found to give nearly agreeing results with the old pro- 
cess. It is much shorter and less expensive, and is recommendetl 
most favorably for practical use, with the suggestion, however, 
that, with every new kind of phosphate or phosphatic fertilizer 
varying notably in composition from the standard, the work should 
be checked at first by comparison with the molybdate method. The 
later investigations carried on by the Association of Official Agri- 
cultural Chemists have served only to confirm the superiority of 
the molybdate gravimetric method for all purposes where great ac- 
curacy is demanded and have shown that for speed and con- 
venience the volumetric method already outlined and later to be 
described in full, is to be preferred to all other quick processes. 

96. The Citrate Precipitate Purity. — Jorgensen recommends the 
following as the safest form of citrate precipitation. The phos- 
phoric acid solution is treated with 25 cubic centimeters of 
neutral ammonium citrate solution or, in case it contains a large 
quantity of calcium salts, with 30 cubic centimeters, and th(MT 
25 cubic centimeters of a 10 per cent, ammonia solution is 
added, and the mixture, in a covered dish, heated to the boil- 
ing point, and, according to the quantity of the phosphate pre- 
cipitate, treated with 30 or 40 cubic centimeters of the neutral 
magnesium chlorid solution. By vigorous stirring or shaking 
the precipitate crystallizes, and after standing at least four 
hours is filtered. If very small quantities of phosphoric acid 
are present the mixture should 1)c left at least 24 hours 

" Die landwirtschaftlichen Veisuchs-Slationen, 1892, 41 : 329. 



\ ■ 
% 






before filtering. In the practice of this method the presence of 
aluminum oxid not exceeding 0.6 gram, or ferric oxid not ex- 
ceeding o.ii gram, may be present, but not in greater quantities 
than these. Calcium oxid should also not be present in quantities 
exceeding 0.03 gram. 

Detailed data are given by Jorgensen in connection wath the 
general determinations of all forms of phosphoric acid, but they 
do not differ sufficiently from those already cited to warrant 
their insertion in full in this manual. The student who desires to 
study in complete detail this latest contribution to the methods 
cf determining phosphoric acid should consult the original article.''^ 
97. The Citrate Method Applied to Samples with Small Content 
of Phosphoric Acid.— It is well established that the citrate method 
does not give satisfactory results when applied to samples con- 
taining small percentages of phosphoric acid, especially when 
these are of an organic nature, as, for instance, cottonseed cake- 
meal. An attempt has been made to remedy this defect in the 
process so as to render the use of the method possible even in 
such cases.'^ Satisfactory results have been obtained by adding 
to the solution of the cake-meal a definite volume of a phosphate 
solution of known strength. Solutions of ordinary mineral phos- 
phates are preferred for this purpose. The following example will 
show the application of the modified method : 

In a sample of cake-meal (cottonseed cake and castor pomace) 
the content of phosphoric acid obtained by the molybdate method 
was 2.52 per cent. 

Determined directly by the citrate method, the following data 

were obtained : 

Allowing to stand 30 hours after adding magnesia mixture, 
T.08 and 1.53 per cent, in duplicates. 

Allowing to stand y2 hours after adding magnesia mixture, 
2.17 and 2.30 per cent, in duplicates. 

In each case 50 cubic centimeters of the solution were used, 
representing half a gram of the sample. 

In another series of determinations 25 cubic centimeters 

^* Zeitschrift fiir aiialytische Cheniie, 1906, 45 : 273. 
"Journal of the American Chemical Society, 1895, 17 : 5^3- 



1; 



ii-i 



41 



CITRATE-SOLUBLE PHOSPHORIC ACID 



107 



106 AGRICULTURAL ANALYSIS 

of the sample were mixed with an equal volume of a mineral 
phosphate solution, the value of which had been previously 
determined by both the molybdate and citrate methods. The 50 
cubic centimeters thus obtained represented a quarter of a gram 
each of the cake-meal and mineral phosphates. The filtration 
followed 18 hours after adding the magnesia mixture. The 
following data show the results of the determinations : 

Percent. Perctnt. Percent. Percent. 

P2O5 in mineral P2O5 in organic PoOr, found in P2O5 in organic 

'phosphate. sample, mixture. sample. 

I 15.37 2.52 17.90 2.53 

2 29.16 2.52 31.68 2.52 

3 31-37 2.52 33.83 2.45 

4 31-58 2.52 34.20 2.62 

Mean content of P2O5 in organic sample 2.53 

It is thus demonstrated that the citrate method can be applied 
with safety even to the determination of the phosphoric acid in 
organic compounds where the quantity present is less than three 
per cent. It is further shown that solutions of mineral phosphates 
varying in content of phosphoric acid from 15 to 32 per cent, 
may be safely used for increasing the content of that acid to 
the proper degree for complete precipitation. In cases where 
organic matters are present they should be destroyed by moist 
combustion with sulfuric acid, as in the determination of nitrogen 
to be described in the next part. 

98. Direct Precipitation of the Citrate-Soluble Phosphoric Acid. 
— The direct determination of the citrate-soluble phosphoric acid 
by effecting the precipitation by means of magnesia mixture in 
the solution obtained from the ammonium citrate digestion,' has 
been practiced for many years by numbers of European chemists, 
and the process has even obtained a place in the official methods 
of some European countries. Various objections have been urged, 
however, against the general employment of this method in fer- 
tilizer analysis on account of the inaccuracies in the results ob- 
tained in certain cases, and it has, therefore, been used to but a 
very limited extent in this country. Since it is impracticable to 
effect the precipitation with ammonium molybdate in the presence 
of citric acid the previous elimination or destruction of this sub- 



stance has been recognized as essential to the execution of a 
process involving the separation of the phosphoric acid as phos- 
phomolybdate. 

It is evident from the data cited in the preceding paragraph, 
that great accuracy may be secured in this process by adding a 
sufficient quantity of a solution of a mineral phosphate and pro- 
ceeding by the citrate method. 

Ross has also proposed to estimate the acid soluble in ammonium 
citrate directly by first destroying the organic matter by moist 
combustion with sulfuric acid.^« He recommends the following 

process : 

After completion of the 30 minutes' digestion of the sample 
with citrate solution, 25 cubic centimeters are filtered at once into 
a dry vessel. If the liquid be filtered directly into a dry burette, 
25 cubic centimeters can be readily transferred to another vessel 
without dilution. After cooling, run 25 cubic centimeters of the 
solution into a digestion flask of 250-300 cubic centimeters capac- 
ity, add about 15 cubic centimeters of concentrated sulfuric acid 
and place the flask on a piece of wire gauze over a moderately 
brisk flame ; in about eight minutes the contents of the flask com- 
mence to darken and foaming begins ; but this will occasion no 
trouble, if an extremely high or a very low flame be avoided. 
In about 12 minutes the foaming ceases and the liquid in the 
flask appears quite black ; about one gram of mercuric oxid is now 
added and the digestion is continued over a brisk flame. The 
operation can be completed in less than half an hour with ease, 
and in many cases, 25 minutes. After cooling, the contents of the 
flask are washed into a beaker, ammonia is added in slight excess, 
the solution is acidified with nitric acid, and after the addition of 
15 grams of ammonium nitrate, the process is conducted as 

usual. 

In case as large an aliquot as 50 cubic centimeters of the 
original filtrate be used, 10 cubic centimeters of sulfuric acid are 
added, and the digestion is conducted in a flask of 300-500 cubic 
centimeters capacity; after the liquid has blackened and foam- 
ing has progressed to a considerable extent, the flask is removed 

'« Division of Chemistry, Bulletin 38, 1893 : 16. 



ill 



fi 



,ft-*».V" ** ta-,.!*.' >j(ti»FJB«-»f«n*« 



I 08 



AGRICULTURAL ANALYSIS 



DETERMINATION OE PHOSPHORIC ACID 



109 



from the flame, 15 cubic centimeters more of sulfuric acid are 
added, and the flask and contents are heated at a moderate tem- 
perature for two or three minutes; the mercuric oxid is then 
added and the operation completed as before described. 

Following are some of the advantages offered by the method 
described : 

(i) It dispenses with the necessity of the frequently tedious 
operation of bringing upon the filter and washing the residue 
from the ammonium citrate digestion, while the ignition of this 
residue together with the subsequent digestion with acid and 
filtration are also avoided. 

(2) It affords a means for the direct estimation of that form of 
phosphoric acid which, together with the water-soluble, consti- 
tutes the available phosphoric acid, thus enabling the latter to 
be determined by making only two estimations. 

(3) In connection with the advantages above mentioned it 
permits of a considerable saving of time as well as of labor 
required in manipulation. 

In addition to the tests with mercuric oxid, both potassium 
nitrate and potassium sulfate are used in the digestion to facil- 
itate oxidation. With the former, several additions of the salt 
are necessary to secure a satisfactory digestion, and even then 
the time required is longer than with the mercury or mercuric 
oxid digestion. With potassium sulfate, the excessive foaming 
which takes place interferes greatly with the execution of the 
digestion process. 

99. Determination of Phosphoric Acid with Preliminary Pre- 
cipitation as Stannic Phosphate. — This method once much in use 
and highly recommended, is now almost unknown among the pro- 
cesses of fertilizer control. It was first proposed by Reynoso and 
modified by Girard, and rests on the precipitation of the phos- 
phoric acid in a nitric acid solution by means of metallic tin.^^ 
The stannic acid formed by the oxidation of the tin unites with 
the phosphoric acid held in a free state by the nitric acid. The 
precipitation of the phosphoric acid is said to be complete, and 
considerable quantities of any iron or alumina which may be pre- 
"' Comptes rendus, 1862, 54 : 468. 



sent are carried down with it. A trace of phosphoric acid has 
been found in the iron and alumina subsequently separated from 
the solution. The precipitate obtained is dissolved in aqua regia, 
made strongly ammoniacal and an excess of ammonium hydrosul- 
fid added. The iron and the alumina are thrown out by this 
treatment. After standing for an hour the precipitate is separat- 
ed by filtration, washed with the ammonium sulfid to remove 
the last traces of tin and the phosphoric acid is separated from 
its filtrate as ammonio-magnesium salt. Following is the second 
method of conducting the analysis as described by Crookes :"* 

The phosphate should be dissolved in nitric acid, and any 
chlorin present be expelled by repeated evaporations with the 
solvent. Finally, to the evaporated mass the strongest nitric 
acid is added. Pure tin foil is added and heat applied. The phos- 
phoric acid is precipitated by the stannic acid formed. The 
(luantity of tin used should be from four to five times as great as 
that of the phosphoric acid present. The preliminary heating 
is indispensable, since in the cold the metal is apt to become pas- 
sive in which state it resists the action of the acid. 

The precipitate is collected on a filter, washed and dissolved 
in caustic potash. The solution is saturated with hydrogen sul- 
fid, and on adding acetic acid in slight excess the tin sulfid is 
separated and removed by filtration. The whole of the phos- 
phoric acid, supposed to be almost free of tin, is now found in 
the filtrate. The filtrate is concentrated to small bulk and any 
tin sulfid present separated by filtering, and the phosphoric acid 
finally removed from the ammoniacal filtrate by precipitation 
with magnesia mixture. The chief difticultics of this method 
are to be found, on the one hand, in the retention of some of the 
phosphoric acid by the iron and alumina which may be present, 
and on the other, in the presence of some tin in the final mag- 
nesium pyrophosphate. If the tin be all removed as sulfid, the 
latter source of error will be avoided. It is difficult to secure pure 
metallic tin, and this is another disturbing element in the process. 

" Select Methods in Chemical Analysis, 4th Edition, 1905 : 497- 



Pi 



on 



AGRICUIyTURAL ANAI^YSIS 



It can not be recommended for the work which agricultural an- 
alysts are usually called on to perform."^® 

100. Phosphoric Acid Soluble in Ammoniuin Citrate.— There is 
no other point connected with the determination of phosphoric 
acid which has excited so much discussion and about which 
there is such difference of opinion as the solubility of phosphates 
in ammonium citrate. It was clearly established by Huston, in 
1882, that the ammonium citrate, as used in fertilizer analysis, 
would attack normal tricalcium phosphate as it exists in bones.^^ 

In a raw bone, finely ground, containing 20.28 per cent, of phos- 
phoric acid, the following quantities are found to be soluble in a 
neutral ammonium citrate solution of 1.09 specific gravity: — 

Time of digestion, thirty minutes. 

Temperature 30° 40° 50° 60° 

Per cent. P2O5 dissolved 2.76 4.01 3.39 5.88 

From this it appears that the quantity of acid dissolved in- 
creases with the temperature of digestion with the exception 
of the number obtained at 50°. When the time of digestion is 
increased there is also found a progressive increase in the amount 
of acid passing into solution. At 40° for 45 minutes the per 
cent, dissolved is 4.97, and 40° for one hour, 5.92. These early 
determinations had the effect of calling attention to the thoroughly 
empirical process which was in use, in many modified forms, by 
agricultural chemists the world over for determining so-called 
reverted phosphoric acid in fertiHzers. Since the publication of 
the paper above named many investigations have been undertaken 
by Huston and others relating to this matter.^^ 

The conditions of solution studied embraced the influence of 
time, temperature, kind and quantity of material, and acidity and 

'» Fresenius, Quantitative Analysis, Cohn's Translation of Sixth German 
Edition, 1904, 1 : 450. 

»« Wiley, 32nd Annual Report of the Indiana State Board of 
Agriculture, 1882 : 225. 

«^ American Chemical Journal, 1884-5, 6 : i. 

Proceedings of the Convention of Agricultural Chemists Atlanta 
Meeting, 1884, Edited by C. W. Dabney, Secretary : 23, 28, 38, 45. ' 
Division of Chemistry, Bulletin 7, 1885 : 18. 
Division of Chemistry, Bulletin 28, 1890 : 171. 
Division of Chemistry, Bulletin 31, 1891 : 99. 



PHOSPHORIC ACID SOLUBLE IN AMMONIUM CITRATE III 

alkalinity of the solvent on the amount of phosphoric acid dis- 
solved. The materials subjected to experiment represented a wide 
range of substances used as, or entering into the composition of, 
photphatic fertilizers such as bone meal, steamed bone, orchilla 
guano, navassa rock, navassa superphosphate, Florida soft rock, 
precipitated calcium phosphate, Pamunky phosphate, calcined 
redonda, South Carolina rock, apatite, grand connetable, acid na- 
vassa. South Carolina phosphate, dissolved bone-black, and cotton- 
seed meal. 

The time of digestion extended from half an hour to 10 hours, 
and in general the quantity of phosphoric acid dissolved by the 
ammonium citrate solution increased as the time of digestion was 

prolonged. 

The digestions were made at temperatures ranging from 30* 
to 85°. In general, the quantity of phosphoric acid dissolved in- 
creased with the temperature. 

The quantity of sample used in its relations to the volume of 
the solvent was also studied. The percentage of the total acid 
dissolved increases very rapidly as the weight of the sample 
diminishes. 

The addition of citric acid to the neutral ammonium citrate 
increases its solvent power. On the other hand, the addition of 
ammonia to the neutral solution of ammonium citrate diminishes 
its solvent power. 

The finer the state of subdivision of the sample the more effi- 
ciently the solvent acts. 

An examination of the original paper of Fresenius, Neubauer, 
and Luck, on whose researches the citrate method is based, shows 
that the temperature conditions are not carefully controlled.®^ An 
attempt has been made to summarize in the above conclusions, 
work made under well defined conditions which illustrate the 
various points under consideration. While each authority of value 
upon the subject is represented, no attempt has been made to dis- 
cuss all the work done by any of them. One element that seems to 
have been generally overlooked in discussing the problem is that 
nearly all results have been obtained from a one-half hour treat- 

»* Zeitschrift fiir analytische Chemie, 1871, 10 : i33- 



IRREGULAR PAGINATION 



112 



AGRICULTURAL ANALYSIS 



DET:eRMINATION OF REVERTED PHOSPHORIC ACID II3 



ment of the material. This means simply the study of an incom- 
plete reaction, and one which is interrupted while the solution is 
very rapidly going on. This, of course, is only clearly brought 
out by comparison of long-time and short-time work in the 
various tables. In the opinion of Huston, much more work 
will have to be done before it can be assumed that we have any 
very clear knowledge of this subject, and probably the conclusion 
will be that all kinds of materials can not be examined by the 
same method. The fact that half a gram of dicalcium phosphate 
is instantly soluble in 100 cubic centimeters of citrate solution, 
at ordinary temperatures, while an equal amount of iron and 
aluminum phosphate is acted upon very slowly at ordinary tem- 
peratures will probably have to be taken into consideration, as 
well as the fact that dicalcium phosphate is less soluble in hot 
solutions of ammonium citrate than it is in cold solutions, while 
the reverse is true of the precipitated iron and aluminum phos- 
phate. 

At present the only conclusion that can be safely drawn from 
the work is that it would be unsafe to make any generalization 
upon the subject until more facts are at hand, except that the 
methods generally in use are unscientific and unsatisfactory. As 
the work progresses, new features present themselves, and in such 
a way as to show that they must be given careful consideration 
before drawing any final conclusions in the matter. At best, it 
must be confessed that the action of a neutral ammonium citrate 
solution on the various forms of phosphates entering into the 
composition of commercial fertilizers is a practically continuous 
process, varying in speed with changing conditions of tempera- 
ture, time, relation of quantity of sample to volume of substance, 
and the fineness of subdivision of the sample. Concordant re- 
sults can therefore only be obtained by observing fixed conditions 
of work. 

loi. Arbitrary Determination of Reverted Phosphoric Acid.— 
The so-called revertc-i i)hosphoric acid, that is, the acid insoluble 
in water and soluble in a solution of ammonium citrate, is the most 
annoying constituent of commercial fertilizers from the point 
of view of the scientific analyst. A review of all the standard 



!: 



ii' 



methods, which have been given in the preceding pages, for its 
determination must convince every careful observer that, as a 
rule, each process is based on arbitrary standards, and can give 
only concordant results when carried out under strictly unvary- 
ing conditions. For this reason there can be no just comparison 
between the results obtained by dilTerent methods, which vary 
from each other only in slight particulars. When, on the other 
hand, the processes are radically different, the deviations in data 
become more pronounced. 

In such a condition of affairs the analyst is left to choose 
between methods. He must be guided in his choice not only by 
what seems to be the most scientific and accurate process, but 
also, to a certain extent, by the general practice of his professional 
brethren. For this country, therefore, it is strongly urged that 
the methods adopted by the Association of Official Agricultural 
Chemists be followed in every detail. 

By the phrase '' reverted phosphoric acid " was originally 
meant an acid once soluble in water, as C3H^(FO^)o, and after- 
wards changed to a form insoluble in water, but soluble in 
ammonium citrate as CaoHo(P04)2. But in practice this has never 
been the true signification of the term. In the manufacture of 
acid- and superphosphates there is formed, more or less of the 
dicalcium phosphate, either directly or after a time, and this salt 
which, in no sense can be called reverted, is entirely soluble in 
ammonium citrate. The iron and aluminum phosphates are also, 
to a certain degree, soluble in the same reagent. When an acid 
phosphate, containing various forms of calcium phosphate, is 
applied to a soil containing iron and alumina, the soluble parts 
of the compound tend to become fixed by union with those bases, 
or by precipitation as CaoH2(P04)o. But it is not alone reverted 
phosphate formed in this way, which the analyst is called on to 
determine in a fertilizer, although he may have occasion to treat 
it in soil analysis. 

The expression 'Veverted phosphoric acid," therefore, in prac- 
tice not only includes a dicalcium phosphate, which once may 
have been the monocalcium salt, but also all of that salt origi- 
nally existing in the superphosphate, and formed directly during 



iHu»d*7nwMjM*flaawaMivNO«4f»i<<0M 



114 



AGRICULTURAL ANALYSIS 



its manufacture, as well as any iron and aluminum phosphates 
present which are soluble in ammonium citrate. It also includes 
any tricalcium phosphate, such as that existing in bones, which 
may pass into solution under the influence of ammonium citrate. 
The expression "citrate-soluble" is, therefore, to be preferred to 
''reverted" phosphoric acid. 

102. Theory of Reversion. — In the reversion of the phosphoric 
acid in superphosphates the iron plays a far more important role 
than the aluminum sulfate. It was formerly supposed that the 
reversion took place as indicated in the following formula : 
2CaH,(POj2+Fe,03=:2(CaHPO,.FeP04)+3HA while Wag- 
rier affirms that the reverted acid compounds consist of vary- 
mg quantities of ferric oxid, aluminum oxid, phosphorus pent- 
oxid, and calcium oxid, in various states of combination.^^ 
The more probable reaction is the following: 3CaH4(P04)2+ 
Fe, ( SO, ) 3+4H,0=2 ( FePO„2H3PO„2H20 ) +3CaS04. This 
reaction can be demonstrated by adding to a superphosphate 
solution one of a ferric salt. In addition to free phosphoric 
acid, iron phosphate is separated, which gradually passes into 
an insoluble form by the abstraction of water due to the crystal- 
lization of the gypsum. The alumina present in a superphos- 
phate seems to have no direct influence on the process of re- 
version. Its phosphate salt is not acted on by the acid calcium 
phosphate. Even when a superphosphate solution is treated with 
alum no precipitation is produced, except on warming, and this 
disappears when the mass is again cold. 

It is therefore not necessary in the process of manufacture 
to separate the alumina by digestion with a hot soda-lye before 
treatinc: the mass with sulfuric acid. 

In order to avoid the reversion of the phosphoric acid several 
plans have been proposed. One of the best is to use a little 
excess of sulfuric acid in the manufacture. This tends to hold 
the phosphoric acid in soluble form, but is objectionable on 
account of drying, handling, and shipping the fertilizer. During 
the digestion, moreover, it is important that the temperature do 
not rise above 120°. Another method consists in adding to the 

**' Lehrbuch der Diingerfabrikation, 



DIGESTION APPARATUS FOR REVERTED PHOSPHATES II 5 



dissolved rock a quantity of common salt chemically equivalent 
to its iron content. Ammonium sulfate also helps to hold the 
phosphoric acid water-soluble. Reversion of the phosphoric acid 
is quite certain to take place in those products where the solvent 
action of the sulfuric acid has not been complete.^* Especially 
is this the case when there are still substances present wdiich can 
be attacked by the acid calcium phosphate. This action is illus- 
trated by the following equation : 

Call, ( PO, ) 2+Ca3 ( PO J ,+8H20=4CaHPO, ( H,0 ) o. 

In this case the undissolved tricalcium phosphate is attacked by 
the acid monocalcium phosphate with the production of a com- 
pound insoluble in water. 

103. Influence of Movement. — The influence of time and tem- 
perature of digestion, and of variations in the composition of 
the ammonium citrate on the quantity of phosphoric acid dis- 
solved by that reagent, has been pointed out. Of great impor- 
tance also in the process is the character of the movement to 
which the materials are subjected during the digestion. For 
this reason various mechanical devices have been constructed to 
secure uniformity of solution. Inasmuch as the temperature fac- 
tor must also be faithfully observed, the best of these devices are 
so arranged as to admit of a uniform motion within a bath of 
water kept at the desired temperature which, by the association 
method, is 65". 

104. Digestion Apparatus for Reverted Phosphates.- — The diges- 
tion apparatus used by Huston consists of two wheels 25 centi- 
meters in diameter, mounted on the same axis, having a clear 
space of four and one-half centimeters between them.®^ In the 
periphery of each wheel are cut 12 notches, which are to re- 
ceive the posts bearing the rings through which the necks of the 
flasks pass. The posts are held in place by nuts which are screwed 
down on the faces of the wheel. Should it become necessary to 

®* Riiiiipler, Kaufliche Diingcstofle und ihre Aiiwendung, 4th Edition, 
1897 : 85. 

^ Indiana Agricultural Experiment Station, Bulletin 54, 1895 : 4. 



■11 

i 1 



|g^!!»»B»!g^«^ M^■a ' '!m ' lewl^«uml^u.JJJ« wl ,«M.,xBu^^ 



ii6 



AGRICULTURAL ANALYSIS 



take the apparatus apart, it is only necessary to loosen the nuts 
and the set screw holdinp^ one wheel to the shaft and all the parts 
can at once be removed. The posts extend lo centimeters beyond 
the face of the wheels, and the rings are four centimeters in inter- 
nal diameter. Perforated plates, bearing a cross-bar, and held in 
place by strong spiral springs attached to the plate and the base of 
the posts serve to hold the flasks in place. Each plate has a number 
stenciled through it for convenience in identifying the flasks 
when it is time to remove them. Attached to the outside of each 
post, close to the outer end, is a heavy wire which passes entirely 
around the apparatus, serving to keep the plates in place after 
they are removed from the flasks. 

The apparatus is mounted on a substantial framework, 36 
centimeters high and 30 centimeters wide at the base. The space ' 
in which the wheel revolves is 14 centimeters wide. The base bars 
connecting the two sides are extended seven centimeters beyond 
one side, and serve for the attachment of lateral bracing. At the 
top of the framework, at one side, is attached a heavy bar 45 centi- 
meters long, which serves to carry the cog gearing which trans- 
mits the power. The upright shaft carries a cone pulley to pro- 
vide for varying the speed. The usual speed is two revolutions 
a minute for the wheel carrying the flasks. The entire apparatus 
is made of brass. The details of construction are shown in Fig. 
6. Round-bottomed flasks are used, and the rubber stoppers are 
held in place by tying or a special clamp shown at the lower 
right-hand corner of the figure. 

When high temperatures are used, the plates and flasks are 
handled by the hooks shown at the left and right-hand upper 
corners of the figure. 

When any other than room temperature is desired, the whole 
apparatus is immersed in water contained in the large galvanized 
tank forming the back-ground of the figure. The tank is 75 
centimeters long, 75 centimeters high, and 30 centimeters wide. 
At one end, near the top, is an extension to provide space for 
heating the fluid in the flasks before introducing the solid, in 
such cases as may be desired. 



Ik 




jF.ig. r6. iHwton's AgitiJ,ti.ng Machii^c. 



ii6 



AGRICULTURAL ANALYSIS 






take the apparatus apart, it is only necessary to loosen the nuts 
and the set screw holding one wheel to the shaft and all the parts 
can at once he removed. The posts extend lo centimeters beyond 
the face of the wheels, and the rings are four centimeters in inter- 
nal diameter. Perforated plates, bearing a cross-bar, and held in 
place by strong spiral springs attached to the plate and the base of 
the posts serve to hold the flasks in place. Each plate has a number 
stenciled through it for convenience in identifying the flasks 
when it is time to remove them. Attached to the outside of each 
post, close to the outer end, is a heavy wire which passes entirely 
around the apparatus, serving to keep the plates in place after 
they are removed from the flasks. 

The apparatus is mounted on a substantial framework, 36 
centimeters high and 30 centimeters wide at the base. The space 
in which the wheel revolves is 14 centimeters wide. The base bars 
connecting the two sides are extended seven centimeters beyond 
one side, and serve for the attachment of lateral bracing. At the 
top of the framework, at one side, is attached a heavy bar 45 centi- 
meters long, which serves to carry the cog gearing which trans- 
mits the power. The upright shaft carries a cone pulley to pro- 
vide for varying the speed. The usual speed is two revolutions 
a minute for the wheel carrying the flasks. The entire apparatus 
is made of brass. The details of construction are shown in Fig. 
6. Round-bottomed flasks are used, and the rubber stoppers are 
held in place by tying or a special clamp show^n at the lower 
right-hand corner of the figure. 

When high temperatures are used, the ])lates and flasks are 
handled by the hooks shown at the left and right-hand upper 
corners of the figure. 

When any other than room temperature is desired, the whole 
aj)paratus is immersed in water contained in the large galvanized 
tank forming the back-ground of the figure. The tank is 75 
centimeters long, 75 centimeters high, and 30 centimeters wide. 
At one end, near the top, is an extension to provide space for 
heating the fluid in the flasks before introducing the solid, in 
such cases as may be desired. 




iF.ig. '6. ;Ht\i^ton's Agitating Ma.chii>€. 



INTENTIONAL SECOND EXPOSURE 



i lm i i i[ ;H iii i| |i r t « «!>y i iii mm p W li g l .'u.) . 11 " I I II »«" I j i "JII»M ll . ' J ii mj 



COMPARISON OF RESULTS 



117 



The apparatus is held in place by angle irons soldered to the 
bottom of the tank and a brace resting against the upright bar 
bearing the gear-wheels. 

The water in the tank is heated by injecting steam, or by 
burners under the tank. As the tank holds about 300 pounds 
of water it is not subject to sudden changes of temperature, 
and little trouble has been experienced in raising and lowering 
the temperature of the water and maintaining it at any desired 
temperature. 

An electric motor, or a small water-motor with only a very 
moderate head of water, will furnish ample power. 

105. Comparison of Results. — The following data show the re- 
sults obtained by the digester as compared with those furnished by 
the official method, temperature and time of digestion being the 
same in each instance. 



Ammonium Citrate Solution on Phosphates. 

Total 



Substance. 



Time 
of 
treatment. 



phos- Removed 
phoric by official 



Steamed bone, 



i yA 



Marl, 



72 
I 

2 

3h 

5 

7^ 
10 

'A 
I 

2 

5 
8 

10 

f y2 



Acidulated bone, <J 2 

I i'A 

L 5 

Bone, A 

Ammoniated diSvSolved bone, }4 

Cottonseed-meal and castor pomace, ^2 

Phospho bone, ^ 



hour 

hours 
( t 



hour 

hours 

( ( 
i t 

t ( 

hour 

hours 
< t 

hour 
( » 



acid. 
Per cent 

27.67 



13-86 



I9-3S 



21.40 

18.22 

2.52 

16.55 



method. 
Per cent. 

IO-59 
12.21 

14.61 

16.48 

17.94 
18.99 

1973 

4.43 
8.28 

10.34 

T 1. 00 

11.80 

12.51 

12.58 

12.09 
12.47 
12.20 
12.40 

12.43 

6.97 
9.28 
0.23 
7.06 



Removed 

by 
digester. 
Per cent. 

14-52 
14.82 

17.56 

18.53 
20.22 

20.25 

21.18 

4. II 
6.82 
9.76 
II. 31 
11.83 
12.64 
13.00 

12 28 
12.40 

12.43 
12.24 

12.26 

8.48 
10.63 

o 25 

7.21 



In comparing duphcates, the results from the use of the 
digester are found to be subject to less variation than those from 
the usual method. It is seen that in many, in fact, the majority 



'I'«s1 



¥ li 






4 
f 



m 



■ ^\ 

''■ H 



Ii8 



AGRICULTURAL ANALYSIS 



of cases, the quantity of phosphoric acid dissolved is markedly 
greater than by the methods where no mechanical stirring is 

employed. 

io6. Huston's Mechanical Stirrer. — The stirring apparatus 
shown in Fig. 7 differs from those which have heretofore come 
into use in requiring but a single belt to drive all the stirring rods, 
and having all the parts protected from the laboratory fumes.^^ 
The details of the belt system are shown in the small diagram in 
the lower central part of the figure. The apparatus is mounted on 
a substantial wooden box, 200 centimeters long, 30 centimeters 
high, and 18 centimeters wide. The driving pulleys, 10 centi- 
meters in diameter, are enclosed in the upper part of the case. 
The shafts on which these pulleys are mounted extend through 




Fig. 7. Huston's Mechanical Stirrer. 

the bottom of the enclosing box and carry a wooden disk, 11 
centimeters in diameter, to prevent particles of foreign matter 
from falling into the beakers. The shafts extend two centimeters 
below these disks, and to the end of the shafts the bent stirring 
rods are attached by rubber tubing. 

The board forming the support of the driving pulleys rs ex- 
tended two centimeters in front of the apparatus, and in this 
extension 12 notches are cut, in which are held the corks carry- 
ing the tubes which contain the solution to be used in precip- 
itating the material in the beakers. 

The ends of these tubes are drawn out to a fine point so as to 
deliver the liquid at the rate of about one drop per second. 

The front of the ap])aratus is hinged and permits the whole to 
be closed when not in use, or during the precipitation. 

®* Indiana Agricultural Kx])erinient vStation, Bulletin 54, 1895 : 7. 



WATER AND CITRATE-SOLUBLE PHOSPHORIC ACID II9 



The apparatus has proven extremely satisfactory in the pre- 
cipitation of ammonium magnesium phosphate. The precipi- 
tate is very crystalline, and where the stirring is continued for 
some minutes, after the magnesia solution has all been added, 
no amorphous precipitate is observed on longer standing. 

107. Precipitation of the Water and Citrate-Soluble Phosphoric 
^cid.— The importance of rapid precipitation with vigorous stir- 
ring when the molybdate solution is employed has also been 
pointed out by Ledoux and likewise the desirability of keeping 
the temperature low (16°).^^ 

In the use of the aqueous and citrate extract of superphos- 
phates the precipitation is conducted as follows : 

The aqueous or citrate extract, or both combined, is made up to 
a volume of 250 cubic centimeters, or each is made up to that vol- 
ume. A part of the solution representing 0.2 gram of the sample 
is boiled with 15 cubic centimeters of strong nitric acid of 1.4 
specific gravity for five minutes to convert all phosphoric acid in- 
to the ortho type. After cooling, 15 cubic centimeters of am- 
monia of 0.92 specific gravity is added, leaving the mixture 
slightly acid, and then 100 cubic centimeters of the molybdic solu- 
tion, prepared by dissolving 150 grams of molybdic acid in 600 
cubic centimeters of ammonia of 0.96 density and pouring the 
solution into 1070 cubic centimeters of nitric acid of 1.22 density. 
The precipitation is made with vigorous stirring, best by a me- 
chanical agitator, for 30 minutes at a temperature not exceed- 
ing 16°. The precipitate is perfectly pure and the phosphoric 
acid may be determined by direct weighing, by titration or by 
the gravimetric process. 

Many of the above precautions were previously pointed out 
by Pellet who especially called attention in 1889 to the volumet- 
ric method of Thilo, afterwards developed by Pemberton and Kil- 
gore.^^ 

»^ Bulletin de 1' Association beige des Chimistes, 1901, 15 : 125. 
'^^ Annates de Chimie analytique, 1900, 5 : 244; 1901, 6 : 248. 

Bulletin de 1 'Association des Chimistes de Sucrerie et de Distillerie, 

1893-94, 11 : 152; 1896-97, 14 : 423. 

Bulletin de 1' Association beige des Chimistes, 1888-89. 3 : 51, 73- 



til 



Pi 






i 



I20 



AGRICULTURAL ANALYSIS 



io8. Veitch's Method for Available Phosphoric Acid. — The gen- 
eral acceptance of the term "available acid" as including both the 
quantity soluble in water and afterwards the additional quantity 
soluble in ammonium citrate solution has led to the suggestion 
that a single determination of the total amount of the dissolved 
acid is, for practical purposes, fully as valuable as the determina- 
tion of the two extracts separately. The usual objection to the 
direct determination of the citrate-soluble acid with the preliminary 
separation with molybdate solution has been the supposed difficul- 
ty of precipitating the phosphoric acid in the presence of a large 
quantity of organic matter, viz., the excess of the citrate used in 
extracting the phosphoric acid. Experience has shown that ac- 
curate separation can be secured, even in the presence of this 
form of organic matter. This fact led Veitch to combine the 
two extracts and determine the so-called available acid in one 
operation. This process is as follows '.^^ 

The two extracts, viz., with water and with ammonium citrate, 
are placed in a 500 cubic centimeter flask with 10 cubic centi- 
meters of nitric acid and the volume completed to the mark. The 
phosphoric acid is determined in aliquots of 100 cubic centimeters, 
whether by the molybdate or direct citrate of magnesia method. 
The precipitates are allowed to stand 18 hours before filtering. 

Comparisons with the official method with many varieties of 
phosphate fertihzers containing from five to 15 per cent, of avail- 
able acid, show close agreement when the molybdate separation 
is used, while by direct precipitation with citrate of magnesia, 
the results are somewhat lower. 

The method therefore possesses certain advantages. Only one 
determination is re(juircd instead of two, and the probable error 
in manipulation is reduced one-half. 

109. Availability of Phosphatic Fertilizers.— There is perhaps 
no one question more frequently put to analysts by practical 
farmers than the one relating to the availability of fertilizing 
materials. The object of the manufacturer should be to secure 
each of the valuable ingredients of his goods in the most useful 
form. The ideal form in which phosphoric acid should come 
*® Journal of Ihe American Chemical Society, 1899, 21 : 1090. 



AVAILABILITY OF PHOSPHATIC FERTILIZERS 



121 



to the soil is one soluble in water. Even in localities where 
heavy rains may abound, there is not much danger of loss of 
soluble acid by percolation. As has before been indicated, the 
soluble acid tends to become fixed in all normal soils and to re- 
main in a state accessible to the rootlets of plants and yet free 
from the danger of exhaustive leaching. For this reason the 
water-soluble acid is regarded by most agronomists as more 
available tlian that portion insoluble in water, yet soluble in 
ammonium citrate. 

In many of the States the statutes, or custom, prescribe that 
only the water and citrate-soluble acid shall be reckoned as avail- 
able, the insoluble residue being allowed no place in the esti- 
mates of value. In many instances such a custom may lead to 
considerable error, as in the case of finely ground bones and some 
forms of soft and easily decomposable tricalcium phosphates. 
There are also, on the markets, phosphates composed largely of 
iron and aluminum salts, and these appear to have an available 
value, often in excess of the quantities thereof soluble in ammo- 
nium citrate. 

As a rule the apatites, when reduced to a fine powder and ap- 
plied to the soil are the least available of the natural phosphates. 
Finely ground bones also tend to give up their phosphoric acid 
with a considerable degree of readiness in most soils. The soft, 
finely ground phosphates, especially in soils rich in humus, have 
an agricultural value, almost if not quite, equal to a similar 
amount of acid in the acid phosphates. Natural iron and alumi- 
num phosphates, have also, as a rule, a high degree of availability. 
Next in order come the land rock and pebble phosphates which, 
in most soils, have only a limited availability. In each case the 
analyst must consider all the factors of the case before rendering 
a decision. Not only the relative solubility of the different 
components of the offered fertilizer in different menstrua must be 
taken into consideration, but also the character of the soil to which 
it is to be applied, the time of application and the crop to be grown. 
By a diligent study of these conditions the analyst may, in the end,, 
reach an accurate judgment of the merits of the sample. 



4' 



mi 



122 



AGRICULTURAL ANALYSIS 



) I 



DIRECT WEIGHING OF THE PHOSPHOMOLYBDATE 

PRECIPITATE 

no. Method of Hanamann. — It has already been stated that 
inany attempts have been made to determine the phosphoric acid 
by direct weighing as well as by titration, as in the Pemberton 
method. Ihe point of prime importance in such a direct de- 
termination is to secure an ammonium phosphomolybdate mix- 
ture of constant composition. Unless this can be done no direct 
method, either volumetric or gravimetric, can give reliable re- 
sults. Hanamann proposes to secure this constant composition 
by varying somewhat the composition of the molybdate mixture 
and precipitating the phosphoric acid under definite conditions.^** 
The molybdate solution employed is prepared as follows : 

Molybdic acid loo grams. 

Ten per cent, ammonia i .o liter. 

Nitric acid ( i .246 sp.gr.) 1.5 liters. 

The precipitation of the phosphoric acid is conducted in the 
cold with constant stirring. It is complete in half an hour. The 
ammonium phosphomolybdate is washed with a solution of ammo- 
nium nitrate and then with dilute nitric acid, dried, and ignited 
at less than a red heat. It should then have a bluish black color 
throughout. Such a body contains 4.018 per cent, of phosphoric 
anhydrid. 

Twenty-five cubic centimeters of a sodium phosphate solution 
containing 50 milligrams of phosphoric acid (PoOJ, treated as 
above, gave a bluish black precipitate weighing 1.249 grams, which 
multiplied by 0.04018, equaled 50.018 milligrams of phosj>horus 
pentoxid. The method should be tried on phosphates of various 
kmds and contents of phosphorus pentoxid before a definite judg- 
ment of its merits is formed. The method is applicable to phos- 
phates containing a large percentage of phosphoric acid as well as 
to compounds having very little. In the former case only a small 
aliquot of the solution is subjected to precipitation, while in the 
latter, all or large portions are used. In one mixture 20 grams of 
superphosphate were dissolved in one liter of water and 10 cubic 
centimeters of the solution poured into 35 cubic centimeters of the 
^ Chemiker-Zeitung, 1895, 19 : 553. 



METHOD OF I^GRKNZ 



123 



molybdate mixture. The precipitate obtained weighed 0.9182 
gram, showing a content of 18.44 per cent, of phosphoric acid in 
the original sample. A gravimetric determination yielded the same 
figure. On the other hand a sample of soil which showed 0.14 
per cent, of phosphoric acid by the gravimetric method, was ex- 
tracted with HNO3 and the acid extract after separation of the 
silica, made up to 100 cubic centimeters and the whole poured 
into the molybdate mixture, gave a content of 0.14082 per cent. 
of phosphoric acid. 

III. Method of Lorenz. — The various methods which have been 
proposed for the direct weighing of the ammonium molybdate pre- 
cipitate of phosphoric acid, have been made the subject of a 
practical and critical study by Lorenz.^^ 

The methods of Meineke, Hanamann, Woy and Hundes- 
hagen are compared and the modifications thereof described. 

The reagents employed by Lorenz are : 

1. Anunonium Molybdate. — This reagent is prepared by pour- 
ing on 100 grams of pure dry ammonium sulfate in a glass cylin- 
der of two liters capacity, one liter of nitric acid of 1.36 specific 
gravity at 15° and stirring until the salt is dissolved. In a liter flask 
300 grams of purest dry ammonium molybdate are dissolved in 
hot water, cooled to about 20° and the flask filled to the mark. 
The contents of the flask are poured in a thin stream with con- 
stant stirring into the solution of ammonium sulfate in nitric acid. 
After standing for at least 48 hours, the solution is filtered and 
stored in a well stoppered bottle kept in the dark. 

2. Nitric acid of 1.20 specific gravity at 15°. 

3. A mixture of sulfuric and nitric acids made by pouring 30 
cubic centimeters of sulfuric acid of 1.84 specific gravity into a 
liter of nitric acid of 1.20 specific gravity. 

4. A two per cent, aqueous solution of pure ammonium nitrate. 

5. Alcohol of from 90 to 95 per cent, strength. 

6. Pure ether. 

The solution of the phosphate is run into a measuring cylinder 
in quantities of 10, 15, or 20 cubic centimeters, according to its 
strength in phosphoric acid and the volume completed to 50 cubic 

" Die landwirtschaftlichen Versuchs-Stationen, 1901, 55 : 183. 



4 



124 



AGRICULTURAL ANALYSIS 



1 1 



i ! 



I i 



! I 



centimeters witii tlie sulfuric-nitric acid mentioned and the 
mixture placed in a ilask of 250 cubic centimeters capacity. The 
mixture is heated and there is added thereto, 50 cubic centimeters 
of the ammonium molybdate reagent. After standing five minutes 
the mixture is stirred vigorously for one minute. The precipi- 
tate is allowed to stand for from three to 18 hours and then 
separated on a gooch under pressure, not through asbestos felt, 
but as recommended by Kilgore, through a disk of ash-free filter 
paper. The last traces of the yellow precipitate are brought 
into the filter and washed several times with the two per cent, am- 
monia nitrate solution. The precipitate is washed three times 
with alcohol and as many times with ether, sucking the filter dry 
after each addition of the washing liquids. When washed and 
dried as described the crucible with its contents is placed in a 
partial vacuum desiccator without CaCL or H2SO4 for 30 min- 
utes and weighed. The ammonium phosphomolybdate prepared 
in this way contains 3.295 per cent, of PoOq. 

112. Method of Woy. — The direct w^eighing of the yellow pre- 
cipitate in the determination of the phosphoric acid in slags ex- 
tracted by citric acid is accomplished by Woy in the following 
manner.^- 

To 50 cubic centimeters of the solution obtained from basic 
slags by treatment with a two per cent, citric acid solution are add- 
<id 30 cubic centimeters of nitric acid of 1. 153 specific gravity, and 
^5 cubic centimeters of ammonium nitrate solution containing 340 
grams of the salt in one liter of water, the mixture boiled and the 
phosphoric acid precipitated by the addition of 100 cubic centi- 
meters of a boiling aqueous six per cent, solution of ammonium 
molybdate. After standing for 15 minutes the supernatant liquid 
u decanted, the precipitate washed with 50 cubic centimeters of 
a solution of 50 grams of ammonium nitrate and 40 cubic centi- 
meters of nitric acid in one liter at a lukewarm temperature and 
then collected on a gooch crucible, dissolved in 10 per cent, am- 
monia, 20 cubic centimeters of ammonium nitrate, 30 cubic centi- 
meters of water and one cubic centimeter of ammonium molybdate 
added to the filtrate, boiled and the yellow precipitate re-formed by 

•' Chemiker-Zeitung, 1903, 27 : 279. 



BKRJU'S MODIFICATION OF P. NEUMANN'S METHOD 1 25 



u > 



the addition of 10 cubic centimeters of nitric acid. The precipi- 
tate is collected in the gooch crucible, washed first with the acid 
ammonium nitrate above described, tlien with alcohol and finally 
with ether. The precipitate is ignited at first gently and then with 
a medium flame until the surface assumes a brilliant crystalline 
deep blue-black appearance. The precipitate is represented by 
the formula 24M03P2O5, and contains 3.946 per cent, of PoO,,. 

Lorenz regrets that the German experiment stations have per- 
sisted in retaining the direct citrate method which is not a strict- 
1\ scientific proceeding, but asserts that his own method of 
drying the yellow precipitate with ether without ignition con- 
sumes less time and is more accurate than Woy's modification as 
given above. "^ 

Sherman and Hyde slightly modify the processes of Woy 
and have been able to obtain results with this method on some 20 
samples of fertilizers, embracing all the common sources of phos- 
phoric acid, which agree within two-tenths of one per cent, with 
results obtained by the molybdate-magnesia method, except in the 
case of a phosphatic slag, in which the variation was three-tenths 
per cent."*"^^ As the precipitate of magnesium pyrophosphate con- 
tained iron, the results by the gravimetric method were probably 
high. The authors use a three per cent, solution of neutral am- 
monium molybdate and add from five to eight cubic centimeters 
of nitric acid to the neutral phosphate solution. The ammonium 
phosphomolybdate is washed with one per cent, nitric acid until 
the washings amount to from 250 to 300 cubic centimeters, and 
ignited at a low heat in the usual way without dissolving and re- 
precipitating. The weight of the phosphomolybdate multiplied by 
0.394Q gives the phosphoric acid. 

113. Berju's Modification of P. Neumann's Method. — Berju calls 
attention to the fact that for at least 10 years it has been well 
known that phosphoric acid could be determined wath great exact- 
ness by the direct weighing of the phosphomolybdate precipitate.®'^ 
During this period the fact has been repeatedly verified. In his 

•^ Chemiker-Zeitung, 19^33, 27 : 495. 

®* Journal of the Atnerican Chemical Society, 1900, 22 : 652. 

^^ Chemiker-Zeitung, 1897, 21 : 441, 469. 

^Journal fiir Landwirtschaft, 1906, 54 : 31. 



'f.ii 



126 



AGRICULTURAI, ANAI^YSIS 



Opinion, none of the methods which have heretofore been pro- 
posed for tliis process has been introduced into the experiment 
stations for the purpose of applying it to the estimation of 
phosphoric acid in fertilizers, these stations having continued to 
follow the time-consuming method of the direct precipitation of 
the phosphoric acid in the citrate solutions, although this method 
has led to no certain results. 

The method of P. Neumann is preferred as the process for 
securing the phosphoric acid, because it requires less time than 
the other methods proposed and is equally exact.^^ Berju, there- 
fore, has applied the principles of this method for general use in 
the investigation of fertilizers containing phosphoric acid. The 
accuracy of the method was first ascertained by its application to 
pure sodium phosphate (Na2HP04+i2H20). For the formula 
of the precipitate he adopts that proposed by Hundeshagen, name- 
ly, i2Alo03P04(NHj3, which contains 3.78 per cent. PsO^.^^ 
The method of procedure is the following: 

Fifty cubic centimeters of the phosphate solution, correspond- 
ing to 0.5 gram of sodium phosphate, are treated with five cubic 
centimeters of nitric acid of 1.2 specific gravity, and with 75 
cubic centimeters of ammonium nitrate-molybdate solution pre- 
pared according to the directions of Wagner-Stutzer, for the pur- 
pose of precipitating the phosphoric acid. The mixture is stirred 
for a quarter of an hour, and after three-quarters of an hour, the 
precipitate is collected upon a gooch after decanting three times 
with about 30 cubic centimeters of the aqueous solution of a five 
per cent, ammonium nitrate solution and one per eent. nitric acid. 
The filtrate is washed six times and the precipitate collected as 
nearly as possible upon the asbestos felt. 

The gooch is placed in a somewhat higher porcelain crucible 
and the precipitate carefully dried over a free fiame, the tempera- 
ture being gradually raised to about 150° to 180° until the 
ammonium nitrate is completely removed. This is determined 
by placing a watch glass upon the top of the crucible for at least 
half a minute and noticing whether any deposit is found thereon. 
•^ Zeitschrift fiir analytische Chemie, 1898, 37 : 303. 
*^ Zeitschrift fiir analytische Chemie, 1889, 28 : 141. 



THE METHOD OF GRAFTIAU 



127 



The dried precipitate is cooled in a desiccator and weighed, cov- 
ered with a watch glass, replaced upon the burner, converted with 
a stronger heat into the phosphomolybdate anhydrid, and cooled 
and weighed as before. The weight of this precipitate multiplied 
by 0.03946 gives the quantity of phosphoric anhydrid (PoOg). 

This method was applied to superphosphates and basic slags. 
In the case of basic slags it was found that the results by the fore- 
going method were accurate, even without the removal of the 
silicic acid. In the illustrations given it appears that after the re- 
moval of the silicic acid there was found 19.30 per cent, of 
P.Og by the direct gravimetric method, while by the weighing of 
the phosphomolybdate precipitate without the separation of the 
silica in two cases the results were 19.35 P^^ cent. PoOg and 19.26 
per cent. PoOg. 

In a determination of the phosphoric acid soluble in a citrate 
solution of basic slag by the direct method, there w^as found 14.7 
per cent, of PsOrj. In the estimation of the same acid after the 
removal of the silicic acid there was found 14.42 per cent, of 
P0O5 by the direct method. Without the removal of the silicic 
acid by direct weighing of the phosphomolybdate precipitate, there 
was found 14.43 P^^ cent, of P2O5. 

The general conclusions of the investigation are : 

1. The methods tried for the estimation of the phosphoric acid 
in fertilizers, depending upon the simplification of the method of 
direct precipitation of the phosphoric acid as i\IgNH4P04, give al- 
most constantly too high results. 

2. The estimation of phosphoric acid as 24M0O3P2O5, accord- 
ing to the method of P. Neumann, gives without exception, very 
exact results, and the use of the different solvents for the phos- 
phoric acid in these fertilizers, as well as the presence of dissolved 
silicic acid in the hydrochloric acid and citrate solutions, are 
without influence on the accuracy of the results. 

Neumann's method is at least more simple and as readily ap- 
plicable as the common method for estimating phosphoric acid as 

Mg^PA- 

114. The Method of Graftiaii. — Graftiau has proposed some 
slight modifications of the method of determining phosphoric 



If 

m 



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w- ■<•; 



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M 



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128 



AGRICULTURAL ANALYSIS 



THE METHOD OF PELLET 



129 



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I' 

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il 



acid by weighing the ammonium phosphomolybdate. His pro- 
cedure is based upon a solution containing a pro|3er content 
of nitric acid, of ammonium nitrate, and ammonium citrate. In 
such a sohition in the presence of an excess of nitromolybdate 
ammonium, the phosphoric acid is precipitated rapidly at a tem- 
perature of about 70°. The precipitate which is formed is pure 
i:nd it is dried upon filter paper without decompiDsition at from 
105° to 110°. 

The method is used particularly in Belgium, where by an 
agreement between ]]elgium, Holland, and the Grand-Duchy of 
l^uxembourg, only two methods of international examination of 
phosphates are permitted, /. c, the direct phosphomolybdate 
method or the citro-magnesium method. The method bv the 
direct weighing of phosphomolybdate ammonium is therefore 
employed only as a means of control in these countries. 

'i he solutions of phosphates are prepared according to the 
methods prescribed by Kuss for the analysis of fertilizing ma- 
terials, cattle feeds, and agricultural products for the Grand- 
Duchy of Luxemlx)urg. 

The acid solutions of the phosphates and basic slags are 
neutralized by ammonium until precipitation commences. The 
precipitate is redissolved by a few drops of nitric acid and 10 
cubic centimeters of PVtermann's citrate of ammonium solution 
added. The rest of the ])rocess is the same as that employed 
where citric acid or ammonium citrate is originally used for 
securing a solution of phosphates soluble therein. 

The phosphoric acid having been thus obtained in the pres- 
ence of a solution of citrate of ammonium, the samples are treated 
as follows : 

There is added to each sample containing from o.i to 0.4 
gram of the original material, according to its richness in phos- 
])horic acid, from two to three cubic centimeters of concentrated 
citric acid from 10 to 15 cubic centimeters of a saturated solu- 
tion of ammonium nitrate, and from 50 to 70 cubic centimeters 
cf water. The mixture is brought to the boiling point, the lamp- 
removed, and there is added from 60 to 100 cubic centimeters 
(according to the richness of the sample) of ammonium nitro- 






molybdate, containing no grams of molybdic acid dissolved in 
400 cubic centimeters of ammonium, 0.96 specific gravity, and 
the solution poured slowly into 1500 cubic centimeters of nitric 
acid of 1.20 specific gravity. The solution is cooled to about 
70" and allowed to rest for 15 to 30 minutes. The precipitate 
sinks very rapidly, leaving a perfectly limpid liquid. The greater 
part of the liquid is siphoned oiY from the precipitate, which 
is afterwards put on a filter and washed two or three times with 
water containing one per cent, of nitric acid. The phospho- 
molybdate of ammonium is then ready to be dried. 

All these operations require very little time because the pre- 
cipitate is already freed from its mother liquors by the liquids 
which have been used for washing out the flasks. 

The precipitate, after removing from the funnel, is first 
placed on filter paper, with care so as not to break the paper, and 
is afterwards transferred to the drying oven where it is dried 
for two hours at a temperature of from 105'' to 110°, as above 
described. 

The different factors which should be used for calculating the 
amount of phosphoric acid from the weight of phosphomolyb- 
date vary among different authors and the factor finally selected 
is 0.0375, which is only slightly different from that proposed by 
Boussingault, i. c, 0.0373-^^ 

115. The Method of Pellet— In 1887 Pellet proposed to the 
French chemists the method of determining phosphoric acid by 
weighing ammonium phosphomolybdate, and this method has 
been employed by a certain number of chemists in France since 
that time.' Pellet is led to believe from the results of his in- 
vestigations that, when precipitated in the presence of a citrate, 
ammonium phosphomolybdate is of constant composition and 
can be accurately dried and weighed on tared filter paper. The 
factor used for calculating the phosphoric anhydrid is 0.0374.- 

^ Atti del VI Coiigresso inteniazionale di Chimica applicata, Roma, 

1' Atti del VI Congresso inteinazionale di Chimica applicata, Roma, 

^^ M^ulk'Un del' Association des Chimistes de Sucrerie et de Distillerie, 
1906-07, 24 : 525- 






^m 



tT 



130 



AGRICULTURAL ANALYSIS 



CLASSIFICATION OF METHODS 



131 



I II 



116. Giadding's Modification. — Gladding- has proposed the 
following modified method for the direct determination of phos- 
phoric acid by weighing the yellow precipitate r^ To the solu- 
tion of phosphoric acid 25 cubic centimeters of strong ammonia, 
0.90 specific gravity, is added, and concentrated nitric acid to 
acidity. The beaker containing the solution is placed in a water 
bath at 50° and the ordinary molybdate solution added at the rate 
of three drops per second in excess and with constant stirring. 
After standing 10 minutes the solution is filtered through a 
weighed filter paper, washed six times with i :ioo nitric acid, 
once with water and dried to constant weight at from 105'' -108° 
m a glycerol or salt water oven. Careful analysis of the dried 
precipitate led to the formula: 24Mo03,I\Or,3(NH4)oO+ 
24Mo( ),, l\,(),,2 ( N H, ) ,0.1 lX)+5} 1,0. 

I.ater Gladding recommended that the yellow precipitate be 
given two final washings w^ith alcohol to facilitate drying.'* This 
method has been examined by the Association of Of^cial Agri- 
cultural Chemists. With slight modifications, such as a gooch 
crucible with a ])ai)cr or asbestos felt for the filtrations, and more 
thorough washing of the precipitate with water (total quantity 
from 100 to 300 cubic centimeters) it has been found to give 
very accurate and trustworthy results.-"' 

VOLUMETRIC DETERMINATION OF PHOSPHORIC ACID. 

117. Classification of Methods. — The time re(|uired for a gravi- 
metric determination of phosphoric acid has led analysts to try 
the speedier, if less accurate processes, depending on the use of 
volumetric methods. The chief difficulty with these methods has 
been in securing combinations of standard composition and some 
sharp method of distinguishing the end reaction. Tn some cases, 
as, for instance, in the uranium method, it has been found neces- 
sary to remove a ])ortion of the titrated solution and prepare it 
lor final testing by subsidence or filtration. As is well known, 
this method of determining the end reaction is less accurate and 
more time-consuming than those processes depending on a change 

" Journal of the American Chemical Society, 1896, 1 8 : 23. 

* Division of Chemistry, Bulletin 51, 1898 : 47. 

* Division of Chemistry, Bulletin 49, 1S97 : 60 ; Bulletin 51, 1898 : 47. 






of color in the whole mass. Free tribasic phosphoric acid can not 
be conveniently titrated directly with a standard alkali, because of 
the development of an amphoteric action near the point of neu- 
trality. When, for instance, an alkali is added to the acid, a com- 
bination is formed of such a character that it will affect an indi- 
cator both as an acid and alkali. All the volumetric processes 
now in general use may be divided into two classes, viz., (i) the 
direct titration of phosphoric acid and the determination of the 
end reaction by any appropriate means, and (2) the previous 
separation of the phosphoric acid, usually by means of a citro- 
niagnesium or molybdenum mixture, and in the latter case the 
subsequent titration of the yellow ammonium phosphomolybdate 
either directly or after reduction to a lower form of oxidation. 
In respect of age and extent of application, by far the most im- 
portant volumetric method is the one depending on titration by a 
uranium salt after previous separation by ammoniacal magnesium 
citrate. A promising method, after previous separation by 
molybdenum, is the one proposed by Thilo and developed by Pem- 
berton, and modified by Kilgore and other members of the Asso- 
ciation of Official Agricultural Chemists, and it has now come into 
cjuite general use in this country. For small quantities of phos- 
phoric acid or of phosphorus, such as are found in steels and irons, 
the method of Emmerton either as originally proposed or as modi- 
fied by Dudley and Noyes, has been frequently used. Where volu- 
metric methods are applied to products separated by molybdic solu- 
tion, the essential feature of the analytical work is to secure a yel- 
low precipitate of constant composition. If this could be uniform- 
ly done in such methods they would rival the gravimetric pro- 
cesses in accuracy. Hence it is highly important in these methods 
that the yellow precipitate should be secured as far as possible 
under constant conditions of strength of solution, duration ot 
time, and manner of precipitation, in these cases, and in such 
only, can the quicker volumetric methods be depended on for 
accurate results. 

The direct volumetric titration of the phosphoric acid by 
a uranium salt or otherwise is practised only when the acid is 
combined with the alkalies and when iron and alinnina are 
absent and only small quantities of lime present. This method 






132 



AGRICULTURAL ANALYSIS 



! ii 



i ' 



has therefore, but little practical value for agricultural purposes. 
In all volumetric analyses the accuracy of the burettes, pipettes, 
and other graduated vessels should be proved by careful calibra- 
tion. Many of the disagreements in laboratories where the 
analytical work is conducted equally well can be due to no other 
cause than the inaccuracy of the graduated vessels which are often 
found in commerce. Burettes should not only be calibrated for 
the whole volume but for at least every five cubic centimeters of 
the graduation. 

URANIUM METHOD AS PRACTISED BY THE FRENCH 

CHEMISTS. 

1x8. The Uranium Method.— Since the phosphoric acid of prac- 
tical use for agricultural purposes is nearly always combined with 
lime, alumina and iron, its volumetric estimation by means of a 
standard solution of a uranium salt is to be preceded by a pre- 
liminary separation by means of an ammoniacal magnesium 
citrate solution. The phosphoric acid may also be separated by 
means of molybdic solution or by tin or bismuth. The principle 
of the method was almost simultaneously pul)lished by Sutton, 
Neubauer, and Pincus.« In practise, however, it has been found 
that when the uranium method is to be used, the magnesium cit- 
rate separation is the most convenient. Since this is the metliod 
until lately practised almost universally in France, it will be given 
in detail. It is based essentially on the process of Joulie,' as 
described by Munro.^ 

119. Preparation of Sample.— (i) Incineration.— ^mce the or- 
ganic matters present in a phosphatic fertilizer often interfere 
with the employment of uranium as a reagent, it is necessary to 
mcmerate the sample before analysis.^ 

(2) Solittwn of the Material.— AW phosphates, with the excep- 
tion of certain aluminum phosphates, amblvgonite for example, 
are easily dissolved in nitric and hydrochloric acids more or less 

Editl^'TiT : ^'^r^ ^''"' ' ••^^'"^' ^^^^^"' Volumetric Analysis. 9th 
Archive fiir vvissenschaftHchc ireilkunde, i860 4 • 228 
Journal fur praktische Chemie, 1859 76 ' 104 ' 

.lor^xr'^^^?^-^"- ^^ ^^ ^^IV^\^ ^^'^' Agricuiteurs de France, 1876 : 53 ; Encv- 
clopcdie chiniKjue, 1888. 4 : 10. > / • dj . ^u^y 

^ Chemical News, 1885, 52 : 85. 

^ Manuel agenda des Fabricants de Sucre, 1889 : 307 



PREPARATION OF SAMPLE 



133 



dilute, especially on ebullition. The best solvent, however, for 
calcium phosphates in the uranium method is incontestably hy- 
drochloric acid which also very easily dissolves the iron and 
aluminum phosphates often found with calcium phosphates. 

(3) Nitric Acid. — In many laboratories nitric acid is preferred 
in order to avoid, in part, the solution of ferric oxid which inter- 
feres with the determination of phosphoric acid in certain pro- 
cesses. Since it does not act in this way for the citro-magne- 
sium uranium method, it is preferable to employ hydrochloric acid, 
especially because it dissolves the iron completely and thus per- 
mits the operator to judge of the success of the solvent action by 
the completely white color of the residue. 

(4) Pyritic Phosphates. — Certain phosphates contain pyrites 
which hydrochloric acid does not readily dissolve, and there is 
left, consequently, a residue more or less colored. In this case it 
is necessary to add some nitric acid and to prolong the boiling 
until the pyrite has disappeared, since it might retain a small 
(juantity of phosphoric acid in the state of iron phosphate. 

(5) Sulfuric Acid. — Some chemists decompose the phosphates 
by means of dilute sulfuric acid. This method, which is cer- 
tainly able to give good results for certain products and for cer- 
tain processes, presents numerous inconveniences tending to 
render its use objectionable for volumetric purposes. The cal- 
cium sulfate formed, requires prolonged washings which lead 
to chances of fatal error. 

If an aluminum phosphate be under examination, containing 
only very little or no lime, sulfuric acid is to be preferred to 
hydrochloric and nitric acids, since it attacks amblvgonite, which, 
as has been before stated, resists the action of the other two acids. 
But these are cases which are met with very rarely, and \yhich 
can always be treated by the general method of previously fusing 
the material with a mixture of sodium and potassium carbonate. 

In the great majority of cases the decomposition by hydro- 
chloric acid is very easily accomplished by simply boiling in a 
glass vessel, and without effecting the separation of the silica. 
This operation is only necessary after the substance has been 
fused with alkaline carbonates, or in case of substances which 



134 



AGRICULTURAL ANALYSIS 



PRECIPITATION OF THE: PHOSPHATE 



135 



contain decomposable silicates giving gelatinous silica with hydro- 
chloric acid. 

There are two methods [see (6) and (7)] of securing a solu- 
tion of the sample which varies from one to fiwe, and even to 10 
grams, according to the apparent quantity of phosphoric acid in 
the material to be analyzed. 

(6) Solution by filtration and Washing. — The ordinary method 
can be employed consisting in decomposing the substance by 
an acid, filtering, washing the residue upon the filter and com- 
bining all the wash-waters to make a determinate volume. After- 
wards an aliquot fraction of the whole is used for the precipita- 
tion. This method is long, and presents some chances of error 
when the insoluble residue is voluminous and contains silica 
which obstructs the pores of the paper and renders the filtration 
difficult. 

(7) Volumetric Solution. — It is advisable to substitute volu- 
metric solution for solution by filtration and washing, which is 
accomplished by decomposing the substance in a graduated flask, 
the volume being afterwards made up to the mark with distilled 
water after cooling. The solution is filtered without washing, 
and by means of a pi])ette an ali(|uot i)art of the original volume 
is removed for analysis. Thus all retardations in the process 
are avoided, and likewise the chances of error from washing on 
the filter. It is true that this method may lead to a certain error 
due to the volume of the insoluble matter which is left undecom- 
posed, but since this insoluble matter is usually small in quantity, 
and since it is always possible to diminish the error therefrom by 
correspondingly increasing the volume of the solution, this cause 
of error is much less to be feared than those due to the difficulties 
which may occur in the other method. Let us suppose, in order to 
illustrate the above, that we are dealing with a phosphate contain- 
ing 50 ])er cent, of insoluble sand which may be considered as an 
extreme limit. In working on four grams of the material in a 
flask of 100 cubic centimeters capacity, there will be an insoluble 
residue of two grams occupying a volume of less than one cubic 
centimeter, the density of the sand being generally above two. The 
100 cubic centimeter flask will then contain more than 99 cubic 



i 



I 



centimeters of the real solution and the error at the most would 
be less than 0.0 1. This error could be reduced to one-half by dis- 
solving only two grams of the material in place of four, or by mak- 
ing the volume up to 200 instead of 100 cubic centimeters. 

In general it may be said that the errors which do not exceed 
o.oi of the total matter under treatment, are negligible for all 
industrial products. The method of volumetric solution does 
not present any further inconvenience. It deserves to be and 
has been generally adopted by reason of its rapidity in all the 
laboratories where many analyses are to be made. In the volu- 
metric method great care should be taken not to make up to the 
volume until after the cooling to room temperature, which may 
be speedily secured by immersing the flask in cold water. Care 
should also be exercised in removing the sample for analysis by 
means of the pipette immediately after filtration, and filtration 
should take place as soon as the volume is made up to the stand- 
ee rd. liy operating in this way the possible variations from 
changes of volume due to changes of temperature are avoided. 

(8) Examination for Arsenic Acid.— When the sample exam- 
ined contains pyrites, arsenic is often present. When the decom- 
position has been effected by means of nitric acid, arsenic acid 
may be produced. This deports itself in all circumstances like 
phosphoric acid, and if it is present in the matter under exami- 
nation, it will be found united with the phosphoric acid and de- 
termined therewith afterwards. It is easy to avoid this cause of 
error by passing first a current of sulfurous acid through the 
solution, carrying it to the boiling point in order to drive out the 
excess of sulfurous acid, and afterwards precipitating the arsenic 
by a current of hydrogen sulfid. After filtration, the rest of the 
operation can be carried on as already described. 

120. Precipitation of the Phosphate in Presence of Citrate. — 
By means of an accurate pipette a quamity of the solution repre- 
senting from 0.125 to 0.250 gram or more is measured, according 
to the presumed richness of the product to be examined. In order 
that the following operations may go on well, it is advisable that 
the quantity of phosphoric acid contained in the sample should be 
about 50 milligrams. The sam])le being measured is run into a 



■i: 



^1, 



136 



AGRICULTURAL ANALYSIS 



beaker, and there are added, first, 10 cubic centimeters of mag- 
nesium citrate solution, and second, a large excess of ammonia, 
li the quantity of the magnesium citrate solution be sufficient, the 
mixture should at first remain perfectly limpid and only become 
turbid at the end of some moments and especially after the mix- 
ture is stirred. 

If there should be an immediate turbidity, it is proof that the 
quantity of magnesium citrate solution employed has been in- 
sufficient to hold the iron and aluminum phosphates in solution 
until the new compounds are formed, and it is necessary to be- 
gin again by doubling its amount. Good results can not be ob- 
tained by adding a second portion of the magnesium citrate solu- 
tion to the original, since the iron and aluminum phosphates which 
are once formed are redissolved with difficulty. Many chemists 
at the present time abstain from using the magnesium citrate solu- 
tion and replace it by a solution of citric acid and one of magne- 
sium sulfate, which they pour successively into the sample under 
examination. This is a cause of grave errors which it is neces- 
sary to point out. Joulie has indeed recognized the fact that 
the precipitation of the phosphoric acid is not completed in pres- 
ence of ammonium citrate unless it is employed in conjunction 
with a sufficient excess of magnesia. But the foreign matters 
which accompany the phosphoric acid require different quanti- 
ties of ammonium citrate in order to keep them in solution, and 
it is important to increase the magnesium solution at the time of 
increasing the citric acid in order to maintain them always in 
the same proportion. This is easily accomplished by measuring 
the two solutions, but it is much more easily done by uniting them 
and adding them together. 

121. The Mag-nesium Citrate Solution. — The formula originally 
proposed by Joulie, modified by Millot, and adopted by the French 
Association of Chemists, is as follows : Citric acid, 400 grams ; 
pure magnesium carbonate, 40 grams ; caustic magnesia, 20 grams ; 
distilled water, half a liter. After solution, add enough of am- 
monia to render .strongly alkaline, requiring about 600 cubic 
centimeters. Make the volume up with distilled water to one 
and a half liters. If the solution be turbid, it is proof that the 



FILTRATION AND WASHING 



137 



magnesia or the carbonate employed contains some phosphoric 
acid, which is to be separated by filtration, and the solution can 
then be preserved indefinitely. 

This solution is made by the formula given by Sutton as fol- 
lows: Add 27 grams of pure magnesium carbonate by degrees 
to a solution of 270 grams of citric acid in 350 cubic centimeters 
of warm water. When all effervescence has ceased and the hquid 
is cooled to room temperature, add 400 cubic centimeters of anv 
nionia of about 0.96 specific gravity, containing approximately 
10 per cent, of NH,. The volume is made up to one liter and kept 
in a well stoppered bottle. ^"^ 

122. Time of Subsidence. — When the phosphoric acid is precipi- 
tated by the mixture above mentioned, it is necessary to allow it 
to subside for a certain time under a bell jar in order to avoid the 
evaporation of the ammonia. In order to give plenty of time 
for this subsidence, it is well to make the precipitations in the 
afternoon and the filtrations the following morning. There are 
thus secured from 12 to 15 hours of repose, which is time amply 
sufficient for all cases. 

123. Filtration and Washing.— Filtration is performed easily 
and rapidly upon a small filter without folds placed in a funnel 
with a long stem of about two millimeters internal diameter. 
Placed in a series of six or eight, they allow the filtration to take 
place in regular order without loss of time, the first filter being al- 
ways empfy by the time the last one is filled. The supernatant 
li(|uid from the precipitate should first be decanted on the filter, 
avoiding the throwing of the filtrate on the filter, which would 
greatly retard the process, especially if it should contain a little 
silica, as o/ten happens. 

When the clear liquid is thus decanted as completely as possi- 
ble, the rest of the precipitate is treated with water to which one- 
tenth of its volume of ammonia has been added, and the washing 
is continued by decantation as at first, and afterwards by wash- 
ing upon the filter until the filtered solution gives no precipitate 
with sodium i)hosphate. Four washings are generally sufficient 
to attain this result. 

^® Sutton. Volutiietric Analysis, 9th Edition, 1904: 299. 



ki 



ni 






f'n 



! 



Mi 



*• ill 



I3S 



AGRICULTURAI. ANALYSIS 



TYPICAI^ SOLUTION OF PHOSPHORIC ACID 



139 



If the operations which precede have been well conducted, the 
total phosphoric acid contained in the material under examina- 
tion is found uix)n the filter paper, except che small portion which 
remains adhering to the beaker in which the precipitation has 
been made. The determination of the phosphoric acid comprises 
the following operations: First, solution of the ammonium mag- 
nesium phosphate, and second, titration by means of a standard 

solution of uranium. 

124. Solution of the Ammonium Mag^nesium Phosphate.— The 
phosphate which has been collected upon the filter is dissolved by 
a 10 per cent, solution of pure nitric acid. This solution is caused 
to pass into the beaker in which the precipitation was made in 
order to dissolve the particles of phosphate which remain adherent 
to its sides ; and this solution is then thrown upon the filter. The 
filtrate is then received in a flask of about 150 cubic centimeters 
capacity, marked at 75 cubic centimeters. After two or three 
washings with the acidulated water, the filter itself is detached 
from the funnel and introduced into the vessel which contains 
the-solution. 

The whole of the filtrate being collected in the flask, it is sat- 
urated bv one-tenth ammoniacal water until a slight turbidity is 
produced. One or two drops of dilute nitric acid are now added 
until the liquor becomes limpid, and the flask is placed upon a 
sand-bath in order to carry the liquid to the boiling-point. After 
ebullition there is added five cubic centimeters of acid sodium 
acetate so as to cause the free nitric acid to disappear, and 
immediately the titration, by means of a standard solution of 
uranium, is undertaken. 

125. Acid Sodium Acetate. — The acid sodium acetate is prepared 
as follows : Crystallized sodium acetate, 100 grams ; glacial acetic 
acid, 50 cubic centimeters; distilled water, enough to make one 
liter. 

126. Standard Solution of Uranium Nitrate. — A solution of ura- 
nium is to be ])repared as follows : Pure uranium nitrate, 40 
grams ; distilled water, about 800 cubic centimeters. Dissolve 
the uranium nitrate in the distilled water and add a few drops of 
ammonia until a slight turbidity is produced, and then a sufficient 



amount of acetic acid to cause this turbidity to disappear. The 
volume is then completed to one liter with distilled water. 

The uranium nitrate often contains some uranium phosphate 
and some ferric nitrate. It is important that it be freed from 
these foreign substances. This is secured by dissolving it in dis- 
tilled water and precipitating it by sodium carbonate, which re- 
dissolves the uranium oxid and precipitates the iron phosphate 
and oxid. 

The filtered liquor is saturated with nitric acid and the uranium 
oxid reprecipitated by ammonia. It is washed with distilled water 
bv decantation and redissolved in nitric acid, as exactly as possi- 
ble, evaporated, and crystallized. 

The crystals are taken up with ether, which often leaves behind 
a little insoluble matter. The solution is filtered, and the ether 
evaporated. The salt which remains is perfectly pure. 

It frequently happens when the uranium nitrate has not been 
properly purified that the solution, prepared as has been indicated 
above, deposits a light precipitate of phosphate which alters its 
strength and affords a cause of error. 

Only those solutions should be employed which have been pre- 
pared some days in advance and which have remained perfectly 
limpid. The solution of uranium thus obtained contains uranium 
nitrate, a little ammonium nitrate, a very small quantity of ura- 
nium acetate, some ammonium acetate, and a little free acetic 
acid. Its sensibility is the more pronounced as the acetates pres- 
ent in it are less in quantity. It is important, therefore, never to 
prepare the solution w^ith uranium acetate. 

127. Typical Solution of Phosphoric Acid. — In order to titrate a 
solution of uranium, it is necessary to have a standard solution 
of phosphoric acid ; that is to say, a solution containing a precise 
and known quantity of that acid in a given volume. This solu- 
tion is prepared by means of acid ammonium phosphate, a salt 
which is easily obtained pure and dry. Sometimes it may con- 
tain a small quantity of neutral phosphate, which modifies the 
relative ])roportions of phosphoric acid and ammonia, and it is 
indispensable to have its strength verified. The titer of the typical 
solution should be such that it requires for the precipitation of 






J M 



- 1 1 

111 



« 14' 






'is 






140 



AGRICULTURAL ANALYSIS 



the phosphoric acid which it contains, a volume of the solution 
of uranium almost exactly equal to its own, in order that the 
expansions or contractions which the two liquors undergo, by rea- 
son of changes in the temperature of the laboratory, should be 
without influence upon the results. 

The solution of uranium, prepared as has been indicated above, 
precipitates almost exactly five milligrams of phosphoric acid per 
cubic centimeter; the typical solution of phosphoric acid is pre- 
pared with eight and one-tenth grams of acid ammonium phos- 
phate pure and dry, which is dissolved in a sufficient quantity of 
distilled water to make one liter. 

Since the acid ammonium phosphate contains 61.74 per cent, 
of anhydrous phosphoric acid, the quantity above gives exactly 
five grams of that acid in a liter, or five milligrams in a cubic 

centimeter. 

Instead of this solution the following is also recommended: 
Dissolve 3.087 grams of pure ammonium phosphate in water and 
make the volume up to one liter. Each 20 cul)ic centimeters of 
this solution corresponds to 0.04 gram of phosphoric anhydrid. 

128. Salt for Setting the Uranium Solution. — In determining the 
strength of the uranium solution the crystallized sodium salt, 
NaoHP04.H.O, has been used. This salt easily loses water and 
for this reason its weight is not constant. Muller proposes to 
use in its place, the acid sodium-ammonium salt, NaHNH4P04. 
4H2O. Even better results are secured by using the crystallized 
(licalcium salt, Ca]IP04.2HoO, which in the free air or even 
over phosphoric anhydrid docs not vary at ordinary tempera- 
tures.^^ 

In the preparation of this salt a solution of disodium phos- 
phate, XaJlPO^, is added little by little to a dilute solution of cal- 
cium chlorid until the lime is almost completely precipitated. 
The gelatinous precipitate at first formed soon becomes crystalline, 
and it is easy to wash it thoroughly. The washed salt is placed 
on plates and dried at 70°. Theoretically, the salt thus obtained 
contains 41.27 per cent, of PoO^. 

129. Verification of the Strength of the Standard Solution of 
Phosphoric Acid. — The strength of the standard solution of phos- 
" Bulletin de la Society chimique de Paris, 1901, [3"], 25 : 1000. 



TITRATION OF SOLUTION OF URANIUM 



141 



phoric acid is verified by evaporating a known volume, 50 cubic 
centimeters, for example, with a solution of ferric hydroxid con- 
taining a known quantity of ferric oxid. The mass having been 
evaporated to dryness and ignited in a platinum crucible, gives 
an increase in the weight of the iron oxid exactly equal to the 
amount of anhydrous phosphoric acid contained therein, both the 
nitric acid and ammonia being driven oi¥ by the heat. 

To prepare the solution of ferric hydroxid, dissolve 20 
grams of iron filings in hydrochloric acid. The solution is filtered 
to separate the carbon, and it is converted into ferric nitrate by 
nitric acid ; then the solution is diluted with distilled water and the 
ferric oxid precipitated by a slight excess of ammonia. The pre- 
cipitate, w^ashed by decantation with distilled water until the 
wash-water no longer gives a precipitate with silver nitrate, is 
redissolved in nitric acid and the solution is concentrated or di- 
luted, as the case may be, to bring the volume to one liter. 

In order to determine the quantity of ferric oxid which it con- 
tains, 50 cubic centimeters are evaporated to dryness, ignited, 
and weighed. 

A second operation like the above is carried on by adding 50 
cubic centimeters of the standard solution of phosphoric acid, 
and the strength of the solution thus obtained is marked upon 
the flask. 

If the operation has been properly carried on, three or four du- 
plicates will give exactly the same figures. If there are sensible 
differences, the whole operation should be done over from the 
first. 

130. Titration of the Solution of Uranium. — In a 150 cubic cen- 
timeter flask marked at 75 cubic centimeters, are poured 10 
cubic centimeters of the standard solution of phosphoric acid 
measured with an exact pipette ; five cubic centimeters of the acid 
sodium acetate are added, and distilled water enough to make 
al3out 30 cubic centimeters, and the whole carried to the boil- 
ing-point. The titration is then carried on by allowing the solu- 
tion of uranium to fall into the flask from a graduated burette, 
thoroughly shaking after each addition of the uranium, and try- 
ing a drop of the liquor with an equal quantity of a 10 per cent. 









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AGRICULTURAL ANALYSIS 



TITRATION OF THE SOLUTION OF URANIUM 



143 






solution of potassium ferrocyanid upon a greased white plate. 
vSince the quantity of the uranium solution present will be very 
nearly 10 cubic centimeters at first, nine cubic centimeters can 
be run in without testing. Afterwards, the operation is continued 
by adding two or three drops at a time until the test upon the 
white plate with the potassium ferrocyanid shows the end of the 
reaction. When there is observed in the final test a slight change 
of tint, the llask is filled up to the mark with boiling distilled 
water and the process tried anew. If in the first part of the opera- 
tion the point of saturation has not been passed, usually the ad- 
dition of a drop or two of the uranium solution is required in order 
to produce the characteristic reddish coloration, and this increase 
is rendered necessary by the increase in the volume of the li(iuid. 
Proceeding in this manner two or three times assures the attain- 
ment of extreme precision, inasmuch as the analyst knows just 
when to look for the point of saturation. 

Correction. — The result of the preceding operation is not abso- 
lutely exact. It is evident, indeed, that in addition to the quantity 
of uranium recjuired for the exact ])reci])itati()n of the phosphoric 
acid, it has been necessary to add an excess sufficient to produce 
the reaction upon the potassium ferrocyanid. 

This excess is rendered constant by the precaution of operating 
always upon the same volume, namely, 75 cubic centimeters. It 
can be determined then, once for all, by making a blank deter- 
mination under the same conditions but without using the phos- 
phoric acid. 

The result of this determination is that it renders possible the 
correction, which it is necessary to make, by subtracting the quan- 
tity used in the blank titration from the preceding result in 
order to obtain the exact strength of the uranium solution. 

The operation is carried on as follows : In a flat-bottomed 
flask of about 150 cubic centimeters capacity and marked at 
75 cubic centimeters, by means of a pipette, are placed 
five cubic centimeters of the solution of sodium acetate : some 
hot distilled water is added until the flask is filled to the mark, 
and it is then placed upon a sand-bath and heated to the boiling- 
point. It is taken from the fire, the volume made up to 75 



i' ■ 

I 



cubic centimeters with a little hot distilled water, and one 
or two drops of the solution of uranium are allowed to flow into 
the flask from a graduated burette previously filled exactly to 
zero. After each drop of the solution of uranium, the flask is 
shaken and the liquid tried upon a drop of potassium ferrocyanid, 
as has been previously indicated. For a skilled eye, four to six 
drops are generally necessary to obtain the characteristic colora- 
tion, that is, from two-tenths to three-tenths of a cubic centi- 
meter. Beginners often use from five-tenths to six-tenths, and 
sometimes even more. 

The sole important point is to arrest the operation as soon as 
the reddish tint is surely seen, for afterwards the intensity of the 
coloration does not increase proportionally to the quantity of 
liquor employed. 

It is well to note that at the end of some time the coloration 
becomes more intense than at the moment when the solutions 
are mixed, so that care must be taken not to pass the saturation- 
point. This slowness of the reaction is the more marked as there 
is more sodium or ammonium acetate in the standard solutions. 
This is the reason that it is important to introduce always the 
same quantity, namely, five cubic centimeters. This is also the 
reason why the uranium acetate should not be employed in pre- 
paring the standard solution of uranium which ought to contain 
the least possible amount of acetate in order that the necessary 
(juantity which is carried into each test should be as small as 
j)0ssible and remain without appreciable influence. If it were 
otherwise, the sensibility of the reaction would be diminished 
in proportion as a larger quantity of uranium solution was em- 
ployed, giving rise to errors which would be as much more im- 
portant as the quantities of phosphoric acid to be determined were 
greater. The correction for the uranium solution having been 
determined, it is written upon the label of the bottle containing it. 

Causes of Error. — In the work which has just been described, 
some causes of error may occur to which the attention of analysts 
should be called. 

The first is the error which may arise from the consumption 
of the small quantity of uranium phosphate which is taken with 



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AGRICULTURAL ANALYSIS 



a Stirring rod when the Hquid is tested with potassium ferro- 
cyanid. It is very easy to be assured that the end of the reaction 
has really been reached. For this purpose it is only necessary to 
note the quantity of the solution already employed and to add to 
it afterwards four drops ; shake, and make a new test with a drop 
of the potassium ferrocyanid placed near the spot which the last 
one occupied. If a decidedly reddish tint does not appear at the 
moment of removing the glass rod, it is to be concluded that the 
first appearance was an illusion, and the addition of uranium is 
to be continued. If, on the contrary, the coloration appear of a 
decided tint, the preceding number may be taken for exact. It 
is then always beneficial to close the titration by this test of four 
supplementary drops which will exaggerate the coloration and 
confirm the figure found. 

The second cause of error, and one, moreover, which is the most 
frequently met with, consists in passing the end of the reaction 
by adding the uranium too rapidly. In place of giving then a 
coloration scarcely perceptible, the test with the drop of potas- 
sium ferrocyanid gives a very marked coloration. In this case 
the analysis can still be saved. For this purpose the analyst has 
at his disposal, a tenth-normal solution prepared with lOO cubic 
centimeters of the standard solution of phosphoric acid diluted to 
one liter with distilled water. Ten cubic centimeters of this tenth- 
normal solution are added, and the titration continued. At the 
end, the amount of additional phosphoric acid used is subtracted 
from the total. 

A third cause of error is found in the foam which is often found 
in the liquid, due to shaking. This foam may retain a por- 
tion of the last drops of the solution of uranium which fall upon 
its surface and prevent its mixture with the rest of the liquid. 
If the glass stirring rod in being removed from the vessel, pass 
through this froth charged with uranium, the characteristic col- 
oration is obtained before real saturation is reached. Conse- 
quently it is necessary to avoid, as much as possible, the forma- 
tion of the foam, and especially to take care never to take the 
drop for test after agitation except in the middle of the liquid, 
where the foam does not exist. 



TITRATION OF SAMPLE 



145 



I' 



Suppose the titration has been made upon 10 cubic centime- 
ters of the normal solution of phosphoric acid in the conditions 
which we have just indicated, and the figure for the uranium 
obtained is 10.2 cubic centimeters; if now the correction, which 
may be supposed to amount to two-tenths cubic centimeter, be 
subtracted there wall remain 10 cubic centimeters of the uranium 
solution which would have precipitated exactly 50 milligrams 
of phosphoric acid. 

The quantity of phosphoric acid which precipitates one cubic 
centimeter of the solution will be consequently expressed by the 
proportion 50^10=5 milligrams, which is exactly the strength re- 
quired. In the example which has just been given, the inscrip- 
tion upon the flask holding the standard solution would be as 
follows: Solution of uranium, one cubic centimeter equals five 
milligrams of phosphorus pentoxid ; correction, two-tenths cubic 
centimeter. 

131. Titration of the Sample.— The strength of the solution of 
uranium having been exactly determined, by means of this solution 
the strength of the sample in which the phosphoric acid has been 
l)reviously prepared as ammonium magnesium phosphate is as- 
certained. In this case the quantity of phosphoric acid being un- 
known, it is necessary to proceed slowly and to duplicate the tests 
in order not to^pass beyond the point of saturation. From this 
there necessarily results a certain error in consequence of the 
removal of quite a number of drops of the solution of the sample 
before the saturation is complete. It is, therefore, necessary to 
make a second determination in which there is at once added 
almost the quantity of the solution of uranium determined by 
the first analysis. Afterwards the analysis is finished by addi- 
tions of very small quantities of uranium until saturation is 
reached. Suppose, for instance, that the sample was that of a 
mmeral phosphate, five grams of which were dissolved in 100 
cubic centimeters, and of which 10 cubic centimeters of the solu- 
tion prepared as above, required 15.3 cubic centimeters of the 
standard solution of uranium. We then would have the following 
data : 









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146 



AGRICULTURAL ANALYSIS 



SOLUBLE AND REVERTKD PHOSPHORIC ACID 



H7 



Mineral phosphate, fiwc grams of the material dissolved m 
20 cubic centimeters of hydrochloric acid. 

Water, sufficient quantity to make 100 cubic centimeters. 

Quantity used, 10 cubic centimeters=o.50 gram of the sample 
under examination. 

Solution of uranium required 15-3 cubic centimeters. 

Correction _^ ^''^'^ centimeters. 

Actual quantity of uranium solution 15.1 cubic centimeters. 

Strength of the solution of uranium, one cubic centimeterzufive 

milligrams P2O5. 

Then P,0,, in 0.50 gram of the material = 5 X I5-^ = 75-5 

milligrams. 

75.5 X 100 _ 
Then the per cent, of PjO^ = "~^ —15. 10. 

The sample under examination ought always to be prepared in 
duplicate, either by making a single precipitation and re-solution 
of the ammonium magnesium phosphate which is made up to a 
certain volume and an aliquot portion of which is taken for the 
analysis, or by making two precipitations under the conditions 
previously described. When the content of phosphoric acid in 
the material under examination is very nearly known, the double 
operation may be avoided, especially if it be required to have 
rapid and only approximate analyses, such as those which are 
made for general control and for the conduct of manufacturing 
operations. But when analyses are to be used to serve as tho 
basis of a law action or for the control of a market, they should 
always be made in duplicate, and the results ought not to be ac- 
cepted when the numbers obtained are widely different, since the 
agreement of the two numbers will tend to show that the work 
has been well executed. 

This method of analysis, much longer to describe than to exe- 
cute, gives results perfectly exact and always concordant when 
it is well carried out, provided that the standard solutions upon 
which it rests for its accuracy are correctly prepared and fre- 
quently verified in the manner indicated. 

The strength of the solution of uranium ought to be verified 



s ■ 



every three or four days. The strength of the standard solution 
of phosphoric acid should be verified each time that the tempera- 
ture of the laboratory undergoes any important change. A solu- 
tion prepared, for example, in winter when the temperature of 
the laboratory is from 15° to 18°, would no longer be exact in 
summer when the temperature reaches 28° or 30°. 

132. Volumetric Determination of Phosphoric Acid in Super- 
phosphates. — Superphos])hates are the products of the decomposi- 
tion of phosphates by sulfuric or hydrochloric acid. They con- 
tain phosphoric acid combined with water, with lime, with magne- 
sia, and with iron and alumina in various proportions. 

These combinations may be classed in three categories : First, 
those compounds of phosphoric acid soluble in w^ater ; second, 
those insoluble in water, but very soluble in ammoniacal salts of 
the organic acids such as the citrate and oxalate ; and third, phos- 
phates not soluble in any of the above named reagents. 

In the products soluble in w^ater are met free phosi)horic acid, 
monocalcium phosphate, acid magnesium phosphate, and the iron 
and aluminum phosphates dissolved in the excess of phosphoric 
acid. In the products insoluble in water but soluble in the am- 
monium citrate are found dicalcium phosphate and iron and 
aluminum i)hosphates, which together constitute the phosphates 
called reverted. 

These compounds reduced to a very fine state of division in the 
process of manufacture are considered to contain ])hosphoric acid 
of the same economic value as that soluble in water. 

133. Determination of the Total Phosphoric Acid in Superphos- 
phates and Fertilizers. — The ])rocess is carried on exactly as fot 
an ordinary phosphate, and with all the care indicated in connec- 
tion with the sam])ling, the incineration, the solution by meari.-> of 
hydrochloric acid, and the separation of the phosphoric acid in the 
state of ammonium magnesium phosphate, and finally in the titra- 
tion with uranium nitrate. 

134. Determination of Soluble and Reverted Phosphoric Acid. 
— To make this determination a method a])plicable to all cases 
consists in extracting, at first, the constituents soluble in distilled 
water, and following this operation by digesting the residue in 



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148 



AGRICULTURAI. ANALYSIS 



ammonium citrate. The products soluble in water can be deter- 
mined either separately or at the same time as the products solu- 
ble in the ammonium citrate, without the necessity of mod- 
ifying very greatly the method of operation 

The determination of the total soluble or available phosphoric 
acid comprises, first, the solution of the soluble constituents in dis- 
tilled water; second, the solution of the reverted phosphates in 
ammonium citrate ; third, the determination of the phosphoric acid 
dissolved in the two preceding operations or the determination of 
the part soluble in ammonium nitrate by difference. 

135. Preparation of the Sample for Analysis. — The sample sent 
to the chemical expert is prepared as has been indicated ; that is 
to say, it is poured on a sieve of which the meshes have a diameter 
of one millimeter, and sifted upon a sheet of white paper. The 
parts which do not pass the sieve are broken up either by the 
hand or in a mortar and added, through the sieve, to the first 
portions. The product is well mixed and, in this state, the mass 
presents all the homogeneity desirable for analysis. 

Some fertilizers are received in a pasty state, which does not 
• permit of their being sifted. It is necessary in such a case to 
mix them with their own weight either of precipitated calcium 
sulfate dried at 160° or with fine sand washed with hydrochloric 
acid and dried, which divides the particles perfectly and permits 
of their being passed through the meshes of the sieve. 

136. Extraction of the Products Soluble in Distilled Water. — 
The substance having been prepared as has just been indicated, 
one and a half grams are placed in a glass mortar. Twenty cubic 
centimeters of distilled water are added, and the substance gently 
suspended therein. After standing for one minute, the super- 
natant part is decanted into a small funnel provided with a filter- 
paper and ])laced in a flask marked at 150 cubic centimeters. This 
operation is repeated five times and is terminated by an intimate 
breaking up of the matter with distilled water. When the volume 
of 100 cubic centimeters of the filtrate has been obtained, the 
residue in the mortar is placed on the filter and the washing is 
continued until the total volume reaches 150 cubic centimeters. 
The filtrate is shaken in order to render the liquor homogeneous, 



SOLUTION OF REVERTED PHOSPHATES 



149 



and is transferred to a precipitating glairs of about 300 cubic 
centimeters capacity. 

137. Solution of the Reverted Phosphates by Ammonium Citrate. 
— The filter from the above process is detached from the funnel 
and is introduced into a flask marked at 150 cubic centimeters 
together with 60 cubic centimeters of alkaline ammonium citrate 
prepared in the following manner : 

Pure citric acid, 400 grams. 

Ammonia of 22^ , 500 cubic centimeters. 

The ammonia is poured upon the crystals of citric acid in a 
large dish. The mass becomes heated, and the solution takes place 
rapidly. When it is complete and the solution is cold, it is poured 
into a flask of one liter capacity, and the flask is filled up to the 
mark with strong ammonia. It is preserved for use in a well 
stoppered bottle. The solution must be strongly alkaline. 

The flask in which the filter paper is introduced, together with 
the anmionium citrate, is stoppered and shaken violently in order 
to disintegrate the filter paper and get the reverted phosphates 
in suspension. There are added then about 60 cubic centi- 
meters of distilled water, and the flask is shaken and left for 
12 hours at least, or at most for 24 hours. The volume is 
made up to 150 cubic centimeters with distilled water, and after 
mixture the solution is filtered. 

There are thus obtained two solutions, one with water and one 
with the alkaline ammonium citrate, which can be precipitated 
together or separately, according to circumstances. The usual 
process is to combine equal volumes of 25, 50, or 100 cubic 
centimeters, representing one-quarter, one-half or one gram of 
the material according to its presumed richness, in a precipitat- 
ing flask to which are added from 10 to 20 cubic centimeters of 
the solution of magnesia made up as follows : 

Magnesium carbonate, 50 grams. 
Ammonium chlorid, 100 grams. 
Water, 500 cubic centimeters. 

Hydrochloric acid, 120 cubic centimeters. 

After complete solution of the solid matters in the above, add 









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I50 



AGRICULTURAL ANALYSIS 



lOO cubic centimeters of ammonia of 22° strength, and distilled 
water enough to make one liter. 

The solutions are thoroughly mixed in a precipitating glass, an 
excess of ammonia added, and allowed to stand for 12 hours 
under a bell jar. The phosphoric acid contained in the liquor is 
separated as ammonium magnesium phosphate. It is collected 
upon a small filter, washed with a little ammoniacal water, redis- 
solved, and titrated with the uranium solution in the manner al- 
ready indicated. 

Bsamplc—ThQ following is an example of this kind of a de- 
termination : 

(i) One and one-half grams of the superphosphate and dis- 
tilled water enough to make 150 cubic centimeters. 

(2) Filter pai)er with reverted phosi)hates, Cyo cubic centi- 
meters of ammonium citrate, and a sufficient quantity of distilled 
water to make 150 cubic centimeters. 

Aqueous solution ( i ) 25 cc. ) ^ 2 s gram of the sample. 
Citrate solution (2) 25 cc. ) 

Add magnesium solution 20 cubic centimeters and ammonia 
in excess, and allow from 12 to 24 hours of digestion, then filter 
and wash, dissolve and titrate. 

Required of solution of uranium 8.55 cubic centimeters ( i cubic 
centimeter=5 milligrams P.^O-,). 

Correction, 0.20 to be deducted=:8.35 cubic centimeters. 

8.35X0.005=0.04175 gram P.O- for 0.25 gram of the sample. 
Then 0.041 75-^-0.25 =16.7 per cent. 

From the above data there would be 16.7 per cent, of phos- 
phoric acid soluble in water and in ammonium citrate. 

If it be desirable to have separately the phosphoric acid soluble 
in water, a separate precipitation is made of the aqueous solution 
alone by means of the magnesium citrate solution. The precipi- 
tate washed with ammoniacal water is redissolved and titrated in 
the manner indicated. 

In subtracting from the figures obtained with the two solutions 
together the number obtained for the phosphoric acid soluble in 
water, the number representing the phosphoric acid soluble in 
ammonium citrate alone, is obtained. 



I 



THE AMMONIO-MANGANOUS METHOD 



151 



It is to be noted that the determinations with uranium require 
always two successive titrations. It would therefore be an ad- 
vantage in all operations to precipitate a weight of ammonium 
magnesium phosphate sufficient for allowing this precipitate to be 
dissolved and made up to 100 cubic centimeters, on which amount 
it would be possible to execute two, three or four determinations, 
and thus to obtain a result of great accuracy. 

138. Conclusions. — It has been seen from the above data that 
the French chemists have worked out the uranium volumetric 
method with great patience and attention to detail. Where many 
determinations are to be made it is undoubtedly possible for an 
analyst to reach a high degree of accuracy as well as to attain a 
desirable rapidity by using this method. For a few determina- 
tions, however, the labor of preparing and setting the standard 
solutions required would be far greater than the actual determina- 
tions either by the molybdate or citrate gravimetric methods. For 
control work in factories and for routine work connected with fer- 
tilizer inspection, the method has sufficient merit to justify a com- 
parison with the processes already in use by the official chemists 
of this country. 

The use of an alkaline ammoniacal citrate solution, however, 
for the determination of reverted acid renders any comparison of 
the French method with our own impossible. On the other hand, 
the French method for water-soluble acid is based on the same 
principle as our own ; viz., washing at first with successive small 
portions of water, and thus avoiding the decomposition of the 
soluble phosphates, which is likely to occur when too great a vol- 
ume of water is added at once. 

In the matter of the temperature and time as affecting the sol- 
ubility of reverted acid, the French method is also distinctly in- 
ferior to our own. The digestion is allowed to continue from 
12 to 24 hours, at the pleasure of the analyst, and meanwhile it 
is subjected to room temperature. It is not difficult to see that 
this treatment in the same sample would easily yield disagreeing 
results between 12 hours at a winter temperature and 24 hours at 
summer heat. 

139. The Ammonio-Manganous Method. — The principle of this 



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AGRICULTURAL ANALYSIS 






I)rocess is based on the separation of the phosphoric acid as the 
ammonio-manganous salt and the subsequent oxidation of the 
manganese to peroxid acid/- The quantity of the peroxid is de- 
termined by the titration with hyposulfite of soda of the iodin 
hberated from potassium iodid. After a study of the methods of 
preparing the ammonio-manganous salt according to the proced- 
ures of Otto, Heintz and Gibbs, the following process was adopted 
as the most suitable : To 50 cubic centimeters of a solution of so- 
dmm phosphate, containing about 100 milligrams of phosphoric 
acid, are added 10 cubic centimeters of a 20 per cent, solution of 
ammonium chlorid, 10 cubic centimeters of ammonia, 25 cubic 
centimeters of a solution of ammonium citrate (150 grams citric 
acid, 500 cubic centimeters ammonia and 1000 cubic centimeters 
water), an excess of a manganous salt, and 25 cubic centimeters 
of a 2.5 per cent, solution of magnesium sulfate. 

This mixture shows an immediate yellow coloration, increasing 
little by little to a greenish brown, but preserves its complete lim- 
pidity. After 24 hours the sides of the vessel are found coated 
with colorless brilliant crystals of ammonio-manganous phosphate, 
but even after several days the separation of the phosphoric acid 
is not complete. 

If the reagents employed be hot, a different series of phenomena 
are presented. The yellowish color at first more pronounced, soon 
disappears and while the liquid is boiling, if it be stirred without 
striking the walls of the vessel, there are immediately separated 
brilliant crystals of the salt of a pale rose color. At the end of 
a few minutes the total phosphoric acid is precipitated. The 
analysis is conducted as follows: After covering the liquid, in 
which the phosphoric acid has been separated as above described, 
the contents of the vessel are thrown on a filter and the precipitate 
washed with 100 cubic centimeters of a dilute solution of anmio- 
nium chlorid (0.5 per cent.). The filtration and washing should be 
made rapidly to avoid danger of solution of the crystals, and the 
whole operation should last only a few minutes. 

Insoluble phosphates are first dissolved in an acid and the phos- 
phoric acid thrown out by ammonium molybdate, the yellow 

»2 y.iiKk-Tnan and Motteu, Bulletin de la Societe chiniiuue de Paris, 
1895, [3]. 13 :523. ^ 



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pkmbkrton's volumetric method 



153 



precipitate is dissolved in ammonia, and the solution treated as 
above. 

The crystals of ammonio-manganous phosphate are dissolved 
in dilute hydrochloric acid, the solution, diluted to 300 cubic centi- 
meters, treated with from one to three cubic centimeters of hydro- 
gen peroxid, 20 cubic centimeters of a 10 per cent, solution of 
potassium hydroxid added and boiled for some time to expel an 
excess of the peroxid. 

After cooling, 20 cubic centimeters of 20 per cent, hydrochloric 
acid are added and the solution allowed to stand for some time in 
order to destroy any traces of an alkaline peroxid. After the ad- 
dition of 20 cubic centimeters of a 10 per cent, solution of potas- 
sium iodid, the liberated iodin is titrated by a set solution of 
sodium hyposulfite. The reactions which take place in these 
operations are illustrated by the following equations : The hydro- 
gen peroxid converts the manganous salt into the compound 
i\InoOii=5MnOoMnO. The ammonio-manganous phosphate has 
the composition GNH^MnPO^. When oxidized by hydrogen 
peroxid, it yields three molecules of phosphoric anhydrid, 3P2O5, 
and one molecule of the compound sMnOoMnO. When the 
manganic peroxid is treated with potassium iodid the reaction is : 
SAInO^-f 20HCl-f ioKI=5MnCL+ioKCl+ioI, and lol-f loNa^ 
S.O3 = 5Na,S,Oe -f loNal. Then ToNa.S.Og = lol = sPAv 
From these data^the percentage of P.O^ is readily calculated. 

The method is of interest from the principle involved, but is of 
little practical value because of the necessity of separating the 
phosphoric acid from all insoluble phosphates by the molybdate 
method. The authors have endeavored to avoid this separation 
and express the hope that a direct way may be found. 

THE DETERMINATION OF PHOSPHORIC ACID BY TITRA- 
TION OF THE YELLOW PRECIPITATE 
140. Pemberton's Volumetric Method.— In order to shorten the 
work of determining the phosphoric acid, numerous attempts have 
been made to execute the final determination directly on the yel- 
low precipitate obtained by treating a solution of a phosphate 
with ammonium molybdate in nitric acid. The composition of 
this precipitate appears to be somewhat variable, and this fact 



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THE PROCESS 



155 



has cast doubt on the methods of determination based on its 
weight. ]ts most probable composition is expressed by the fol- 
lowing formula, (NH4)3P04(Mo03)io. For convenience in 
writing reactions this formula should usually be doubled. Pem- 
berton has described a volumetric determination of phosphoric acid 
in the yellow precipitate which is easily conducted and is very 
rapid. ^'^ 

The method as originally proposed by Pemberton has not al- 
ways given satisfactory results when compared with the molyb- 
date gravimetric process, but as perfected by experience has con- 
stantly grown in favor until now it is regarded as entirely trust- 
worthy on account of its original merit and of the extended use 
in later forms. It has, however, attracted so much attention from 
analysts as to the ])rinciples of the original process, that they are 
given in some detail. 

141. The Process. — The principle of the process is based on the 

separation of the phosphoric acid as ammonium-phosphomolyb- 

date, freeing the yellow precipitate from any free nitric acid by 

washing, dissolving the yellow precipitate in an excess of standard 

alkali and titrating the residual alkali by a standard acid. The 

process as originally described by Pemberton is carried out as 

follows : One gram of phosphate rock, or from two to three 

grams of phosphatic fertilizer, are dissolved in nitric acid and, 

without evaporation, diluted to 250 cubic centimeters. Without 

filtering, 25 cubic centimeters are placed in a four-ounce beaker 

and ammonia added until a slight precipitate begins to form. 

Five cubic centimeters of nitric acid of one and four-tenths 

specific gravity are added, and 10 cubic centimeters of saturated 

solution of ammonium nitrate and enough w^ater to make the 

volume about 65 cubic centimeters . The contents of the 

beaker are boiled, and while still hot f\vQ cubic centimeters of the 

aqueous solution of ammonium molybdate added. .Additional 

(juantities of the molybdate are used, if necessary, until the 

whole of the phosphorus pentoxid is thrown out. 

After allowing to settle for a moment the contents of the beaker 
are poured upon a filter seven centimeters in diameter. The pre- 
1=^ Journal of the American Chemical Society, 1893. 15 : 382. 



cipitate is thoroughly washed with water, both by decantation 
and on the filter. The filter with its precipitate is transferred to 
a beaker and dissolved with an excess of standard alkali in the 
presence of phenolphthalein. The residual alkali is determined 
bv titration with standard acid. Each cubic centimeter of alkali 
employed should correspond to one milligram of phosphorus pent- 
oxid (P,0,). 

The reagents have the composition indicated below : 

Ammonium Molybdate. — Ninety grams of the crystals of am- 
monium molybdate are placed in a large beaker and dissolved in 
a little less than one liter of water. The beaker is allowed to stand 
over night and the clear liquor decanted. Any undissolved acid 
is brought into solution in a little ammonia water and added to 
the clear liquor. If a trace of phosphoric acid be present a little 
magnesium sulfate is added and enough ammonia to produce a 
slight alkaline reaction. The volume of the solution is then 
made up to one liter. It is to be observed that nitric acid is not 
used in the preparation of this reagent, which is known as the 
aqueous solution. Each cubic centimeter of this solution is capa- 
ble of precipitating three milligrams of phosphorus pentoxid. 

Standard Potassium Hydroxid. — This solution is made of such 
strength that one cubic centimeter is equivalent to one milli- 
gram of phosj)horus pentoxid. Treated with acid of normal 
strength, 100 cubic centimeters are re(|uire(l to neutralize 32.65 
cubic centimeters thereof. The strength of the solution can not 
be safely assumed from the weight and j)urity of the material, but 
is to be ascertained by comparison with a solution of a phosphate 
of known composition. 

Standard Acid. — This should have the same strength, volume 
for volume, as the standard alkali solution. It is made by dilut- 
ing 326.5 cubic centimeters of normal nitric acid to one liter. 

Ammonium Nitrate. — A saturated aqueous solution of the salt 
is used. 

Indicator. — The indicator to be used is an alcoholic solution of 
phenolphthalein, one gram in 100 cubic centimeters of 60 per 
cent, alcohol, and half a cubic centimeter of this should be used 
for each titration. 



I'i 









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11 



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AGRICULTURAL ANALYSIS 



Thomson has shown that of the three hydrogen atoms in 
phosphoric acid, two must be saturated with alkaU before the 
reaction with phenolphthalein is neutral.^* Therefore, when the 
yellow precipitate is broken up by an alkali, according to the 
reaction to follow, only four of the six molecules of ammonium 
are required to form a neutral ammonium phosphate as determined 
by the indicator employed. The remaining two molecules of 
ammonium unite with the molybdenum, forming also a salt neu- 
tral to the indicator. 

I^hcnolphthalein is preferred because, as has been shown by 
Long, its results are reliable in the presence of ammonium salts 
unless they be present in large quantity, and if the solution be 
cold and the indicator be used in sufficient quantity.^^ To pre- 
pare the indicator for this work, one gram of phenolphthalein is 
dissolved in loo cubic centimeters of 60 per cent, alcohol. At 
least one-half of a cubic centimeter of the solution is used for 
each titration. 

The advantages claimed for the method are its speed and 
accuracy. Much time is saved by avoiding the necessity for the 
removal of the silica by evaporation. The results of analyses 
with and without the removal of the silica are practically identical. 
When the silica is not removed it is noticed that the filtrate 
from the yellow precipitate has a yellow tint. 

The reaction is represented by the following formula: 

(NH,)JPO,),(MoO,).4+46KOH=(NH,),(HPOj2+ 
(NH,),MoO,+23K,MoO,-f22H,0. 

From this reaction it is seen that the total available acidity of 
one molecule of the yellow precipitate titrated against phenol- 
phthalein is equivalent to 23 molecules of potassium hydroxid. 

Calculation of Results.—Tht standard alkali is of such strength 
that one cubic centimeter is equal to one per cent, of phosphoric 
acid when one gram of material is employed and one-tenth of it 
taken for each determination. If in a given case one gram of a 
sample and one-tenth of the solution are used, and 50 cubic cen- 
tuneters of alkali added to the yellow precipitate, it requires 
'* Chemical News, 1883, 47 : 127, 186. 
'^ American Chemical Journal, 1889, 1 1 : 84. 



THE PROCESS . 1 57 

32 cubic centimeters of standard alkali to neutralize the excess 
of acid. 

The alkali consumed by the yellow precipitate represents 50 — 32 
= 18 cubic centimeters. The sample, therefore, contains 18 per 
cent, of phosphoric acid. 

Comparison zvith Official Method. — A comparison of the Pem- 
"berton volumetric with the official method of the Association of 
Official Agricultural Chemists has been made by Day and Bry- 
;}.\\i}^ The comparisons were made on samples containing from 
1.45 to 37.28 per cent, of phosphoric acid and resulted as follows: 

Per cent. Per cent. 

Substance. P2O5, Official. P2O5, Pemberton. 

No. I. Florida rock 1.45 1.32 

" ^- " " 440 4.53 

*' 3. Sodium phosphate 19-78 19-99 

" 4. " " 19.72 19.73 

" 5. Florida rock 37-28 37.22 

This near agreement shows the reliability of the method. The 
•comparison of .the Pemberton volumetric method with the official 
gravimetric method was investigated by Kilgore, reporter of the 
/issociation of Official Agricultural Chemists, in 1894.^^ The 
individual variations were found to be greater than in the regular 
method, but the average results were nearly identical therewith. 
The method works far better with small percentages of phosphoric 
acid than with large. Where the average of the results by the 
•official methods gave 12.-25 P^^ cent., the volumetric process gave 
11.90 per cent., whereas in the determination of a smaller per- 
centage the results were 2.72 and 2.73 per cent., respectively. 
Kilgore proposes a variation of the method which differs from 
the original in two principal points.^** First, the temperature of 
precipitation in the Pemberton process is 100° ; but in the modi- 
fied form from 55° to 60°. At the higher temperature there is 
danger of depositing molybdic acid. 

The second difference is in the composition of the molybdate 
solution employed. The official molybdate solution contains about 

'^Journal of the American Chemical Society, 1894, 16 : 282. 
^^ Division of Chemistry, Bulletin 43, 1894 : 68. 
'^ Division of Chemistry, Bulletin 43, 1894 : 91. 






h 






11 



158 



AGRICULTURAL ANALYSIS 



60 grams of molybdenum trioxid in a liter, while the Pem- 
berton solution contains 66 grams. There is, therefore, 
not much difference in strength. The absence of nitric acid, how- 
ever, from the Pemberton solution favors the deposition of the 
molybdic acid when heat is applied. 

Kilgore, therefore, conducts the analysis as follows : The 
solution of the sample is made according to the official nitric and 
hydrochloric acid method for total phosphoric acid. For the 
determination, 20 to 40 cubic centimeters are used corresponding 
to two-tenths or four-tenths gram of the sample. Am- 
monia is added until a slight precipitate is produced and the 
volume is then made up, with water, to 75 cubic centi- 
meters. Add some ammonium nitrate solution, from 10 to 15 
cubic centimeters, but this addition is not necessary unless 
much of the nitric acid has been driven off during solution. Heat 
in the water bath to 60° and preci])itate with some freshly filtered 
official molybdate solution. Allow to stand for five minutes, filter 
as (juickly as possible, w^ash four times by decantation, using from 
50 to 75 cubic centimeters of water each time, and then wash 
on a filter until all acid is removed. The solution and titra- 
tion of the yellow ])recipitate are accomplished as in the Pem- 
berton method. The agreement of the results obtained by this- 
modified method was much closer with the official </ravimetric 
method than those obtained by the Pemberton process. 

142. Investigations of the Volumetric Method by the Asso- 
ciation of Official Agricultural Chemists. — 1'he great value of the 
volumetric method by reason of the saving of time in analytical 
work, especially where great numbers of analyses are to be made, 
led to a painstaking investigation of its reliability and agreement 
with the gravimetric process on the part of the official chemists. 
' The results of these investigations are published in detail in the- 
proceedings of the association.^" 

'•' Division of Chemistry, Bulletin 47, 1896 : 70. 
Division of Chemistry, Bulletin 49, 1897 : 60. 
Division of Chemistry, Bulletin 51, 1898:47. 
Division of Chemistry, IhilUtin 56, 1899 : 36. 
Division of Chemistry, P.ulUlin 57, 1899 : 69. • ' ' 

Division of Chemistry, lUilletin 62, 1901 : 35. 
Bureau of Chemistry, Bulletin 67, 1902 : 22. 
Bureau of Chemistry, Bulletin 8r, 1904 : 164. 



OPTIONAL VOLUMETRIC METHOD 



159 



These investigations have led to the adoption of the volumetric 
method in the present form, and established its position as a pro- 
cess which can be relied upon to give concordant and reliable re- 
sults. For all ordinary analytical, routine and control work it may 
be confidently used. In cases of controversy, and especially be- 
fore the courts, it is advisable to check the data obtained by the 
volumetric method against the results of the of^cial gravimetric 
determination. The principal credit for perfecting this method 
is due to Kilgore, as is clearly shown by a study of the references 
given. 

143. Optional Volumetric Method. — The principles on which this 
rapid and accurate process is based have been described in detail 
in the discussion of the Pemberton process. The method of con- 
ducting the determination and the reagents employed as prescribed 
by the official chemists are as follows : 

Reagents Used: Molybdic Acid. — To 100 cubic centimeters of 
the molybdic acid solution used in the official gravimetric method 
already described, add five cubic centimeters of nitric acid of 1.42 
specific gravity. If cloudy this solution should be filtered before 
using. 

Potassium or Ammonium Nitrate Solution. — Dissolve three 
grams of the salt in 100 cubic centimeters of water. 

Nitric Acid. — Dilute 100 cubic centimeters of nitric acid of 1.42 
specific gravity to 1000 cubic centimeters with water. 

Potassium Hydrorid. — This solution contains 18. 171 grams of 
KOH in one liter. Tt is prepared by diluting 323.81 cubic centi- 
meters of a normal solution of pure potassium hydroxid, free of 
carbonates, to one liter. One milligram of the solution is equiva- 
lent to one milligram of phosphorus pentoxid. 

Standard Nitric Acid Solution. — The strength of this solution 
is the same as, or one-half that of, the standard alkali solution, 
and is determined by titrating against that solution, using phenol- 
phthalein as indicator. 

Phenolphthalein Solution. — One gram of phenolphthalein is 
dissolved in too cubic centimeters of alcohol. 

Total Phosphoric Acid. Methods of Making Solution. — Dis- 
solve according to the ofiicial methods described in paragraph 61, 



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AGRICULTURAL ANALYSIS 



prefcrablv method 5, when these acids are a suitable solvent, 
and dilute to 200 cubic centimeters with water. 

Determination,— J^ or percentages of phosphoric acid of five or 
below use an aliquot corresponding to 0.4 gram substance; for 
percentages between five and 20 use an aliquot corresponding to 
0.2 gram substance ; and for percentages above 20 use an aliquot 
corresponding to o.i gram substance. Add from five to 10 cubic 
centimeters of nitric acid, depending on the method of solution 
(or the equivalent in ammonium nitrate), nearly neutralize with 
ammonia, dilute to from 75 to 100 cubic centimeters, heat in a 
water bath to from 60° to 65°, and for percentages below five- 
add from 20 to 25 cubic centimeters of freshly filtered molybdic 
solution. For percentages between five and 20 add from 30 to 
35 cubic centimeters molybdic solution; stir, let stand about 15 
minutes, filter at once, wash once or twice with water by decanta- 
tion, using from 25 to 30 cubic centimeters each time, agitating 
the precipitate thoroughly and allowing it to settle; transfer to 
filter and wash five or six times, using enough water to make 
with the decantation washings about 200 cubic centimeters. 
Transfer precipitate and filter to beaker or precipitating vessel, 
dissolve in small excess of standard alkali, add a few drops of 
phenolphthalein solution and titrate excess of alkali with stand- 
ard acid (nitric). 

M^ater-Soluble Phosphoric Acid. — Dissolve the soluble acid ac- 
cording to directions given under the official method for the grav- 
imetric determination of water-soluble acid, paragraph 67. To an 
aliquot portion of the solution corresponding to 0.2 or 0.4 gram, 
add 10 cubic centimeters of concentrated nitric acid and then am- 
monia until a slight precipitate is formed, dilute to 60 cubic 
centimeters, and proceed as above described. 

Citrate-Insoluble Phosphoric Acid. — (a) In Acidulated Sam- 
ples. — Heat 100 cubic centimeters of strictly neutral ammonium 
citrate solution of 1.09 specific gravity to 65° in a flask placed in 
a bath of warm water, keeping the flask loosely stoppered to pre- 
vent evaporation. When the citrate solution in the flask has 
reached 65°, drop into it the filter containing the washed residue 
from the water-soluble phosphoric acid determination, stopper 



: I 



ALKALIMETRIC ESTIMATION 



161 



tightly with a smooth rubber, and shake violently until the filter 
paper is reduced to a pulp. Place the flask in the bath and main- 
tain it at such a temperature that the contents of the flask will 
stand at exactly 65°. Shake the flask every five minutes. At the 
expiration of exactly 30 minutes from the time the filter and 
residue are introduced, remove the flask from the bath and im- 
mediately filter the contents as rapidly as possible. Wash thor- 
oughly with water at 65°. Transfer the filter and its contents to 
a crucible, ignite until all organic matter is destroyed, add from 
10 to 15 cubic centimeters of strong hydrochloric acid, and digest 
until all phosphate is dissolved ; or return the filter with contents 
to the digestion flask, add from 30 to 35 cubic centimeters strong 
nitric acid, from hve to 10 cubic centimeters strong hydrochloric 
acid, and boil until all phosphate is dissolved. Dilute the solution 
to 200 cubic centimeters. If desired, the filter and its contents 
may be treated according to the methods in paragraph 61 under 
methods of solution. Mix well; filter through a dry filter; take 
a definite portion of the filtrate and proceed as under total phos- 
phoric acid. 

{b) In Non-Acidulated Samples.— In case a determination of 
citrate-insoluble phosphoric acid is required in non-acidulated 
samples it is to be made by treating two grams of the phosphatic 
material, without previous washing with water, precisely in the 
way above described, except that in case the substance contains 
much animal maUer (bone, fish, etc.) the residue insoluble in 
ammonium citrate is to be treated by one of the processes de- 
scribed under methods of solution, paragraph 61. 

Citrate-Soluble Phosphoric Acid.— The sum of the water-solu- 
ble and citrate-insoluble subtracted from the total gives the cit- 
rate-soluble phosphoric acid. 

144. Alkalimetric Estimation of Phosphoric Acid in Connection 
with the Incineration by Acid Mixture.— Neumann recommends 
the following process, which is a variation of the ordinary volu- 
metric method in common use in this country for the estimation 
of phosphoric acid in organic matters which have been incin- 
erated by the wet acid method described by him.^o Por carrying 

'° Zeitschnft fiir physiologische Chemie, 1902-3, 37 : 115. 



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AGRICUI.TURAL ANALYSIS 



out this method the substance is incinerated by a mixture of sul- 
furic and nitric acids. From the ash solution obtained by the 
•method described the phosphoric acid is precipitated in the usual 
manner as phosphomolybdate. The washed precipitate is imme- 
diately dissolved in an excess of one-half normal soda-lye and the 
excess of alkali titrated with one-half normal sulfuric acid, after 
driving off the ammonia by boiling and allowing the solution to 
become completely cool. 

Since each molecule of the phosphoric pentoxid (PoOr,) o^ the 
yellow precipitate obtained by this method of treatment requires 
for its complete neutralization, with the use of phenolphthalein 
as an indicator, 56 molecules of NaOH, so each cubic centimeter 
of one-half normal soda-lye used corresponds to 1.268 milligrams 
of P,0,. 

The solutions used by Neumann are as follows : 

( 1 ) 50 per cent, ammonium nitrate solution. 

(2) TO per cent, of ammonium molybdate solution (dissolved, 
cooled, and filtered). 

(3) One-half normal potash lye and one-half normal sulfuric 
acid. 

(4) One per cent, alcoholic phenolphthalein solution. 

The substance is incinerated according to the method described 
and the dilution with water, which is recommended at the close of 
the method, as well as the boiling of the ash solution, are prop- 
erly modified for the special estimation of the phosphoric acid. 

Under the assumption that for the incineration not more than 
40 cubic centimeters of the acid mixture have been used, about 140 
cubic centimeters of water are added to the ash solution, so that in 
all the analyst has in amount from 150 to 160 cubic centimeters. 
It should be remembered in this case that about one-half of the 
acid mixture has been volatiliz.ed during the incineration. After 
the addition of 50 cubic centimeters of ammonium nitrate, the 
mixture is heated to from 70"" to 80° until bubbles begin to 
ascend through the liquid. Thereupon, 40 cubic centimeters of 
ammonium molybdate are added. This cpiantity is sufficient for 
at least 60 milligrams of l\fir,. It is recommended that the quan- 






AI^KALIMKTRIC ESTIMATION 



163 



tity of' substance used be so chosen that it contains not more than 
50 milligrams of phosphoric acid. If more than 40 cubic centi- 
meters of the acid mixture have been used in the incineration, then 
the quantity of water added in the dilution and the quantity of 
ammonium nitrate therein should be proportionately increased. 

The fiask containing the precipitate is vigorously shaken for a 
half minute, by which process the precipitate becomes more 
granular, and it is then allowed to stand at rest for m min- 
utes. The filtering and washing are carried on by decantation. 
Thin, ash-free filter paper is used, which on the subsequent solu- 
tion of the precii)itate in dilute soda-lye is easily torn and the par- 
ticles of which are evenly divided throughout the liquid. The 
filter paper, which has a diameter of from five to six centimeters, 
may be used either as a folded filter or as a smooth filter in a 
lluted funnel. Uefore filtration the filter is filled with ice-cold 
water, in order to draw the filter pores together and to prevent 
the first portions of the solution, which is still warm, from run- 
ning through cloudy. In order to conveniently decant the super- 
natant li(iuid, the flask is laid upon the ring of the stand some- 
what liigher than the filter and the neck is drawn down in such 
a way that the clear licpiid runs withour mtermission u]xyn the 
filter. In this way only a very small quantity of the precipitate 
is collected upon the filter, which is always kept about two-thirds 
full. The washing of the precipitate is conducted with about 
150 cubic centimeters of ice-cold water, which is thoroughly in- 
corporated with the precipitate, and after standing is poured 
through the filter in the way described. The decantation is con- 
tinued with repeated washing with water until the wash-water 
no longer gives an acid reaction with litmus paper. The washed 
tilter and its contents are then put back in the flask containing the 
prmcipal part of the precipitate, 150 cubic centimeters of water 
added, the filter broken up by vigorous shaking, and tlie precipi- 
tate dissolved by adding a measured portion of one-half normal 
potash lye with constant shaking and without warming. It is then 
advisable to add an excess of from five to six cubic centimeters 
of one-half normal soda-lye and to boil the solution until no 
longer any ammonia is evolved, which usually requires about 



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AGRICULTURAL ANALYSIS 



15 minutes and which should be determined by testing with 
moist htmus paper. After complete cooling, from six to eight 
drops of the phenolphthalein solution are added and the excess 
of alkali titrated with one-half normal sulfuric acid. 

Calculation.— The number of added cubic centimeters of one- 
half normal soda-lye, after the subtraction of the number of cubic 
centimeters of one-half normal acid used, multiplied by 1.268, 
gives the quantity of PoO, in milligrams. 

145. Comparison of the Methods of Weighing and Titrating 
the Yellow Precipitate.—Baxter gives the result of his experi- 
ments upon the estimation of phosphoric acid by weighing the 
yellow precipitate after heating to 300° and also by titration with 
standard alkali.-^ 

In securing the yellow precipitate in a form sufficiently pure 
for analytical purposes he states that it can not be washed with 
water owing to decomposition. Ten per cent, ammonium nitrate 
solution is therefore used as a wash, but no data are given to 
prove that washing was carried to the complete removal of the 
molybdate. Indeed, all the results show that the precipitate still 
contains considerable quantities of ammonium molybdate or 
molybdenum oxid. It is stated that the formula of the precipi- 
tate washed. with the ammonium nitrate solution and dried at 300" 
is (NH/),P04.i2MoO;j, but owing to the occlusion of molyb- 
dic acid the theoretical percentage of PoO., (3.783) is never ob- 
tained. The precipitate only contains 3.742 per cent, of phos- 
phoric acid. 

In the second article evidence is given to show that the washed 
unhcated yellow precipitate has the formula (NH4)2HP04.- 
i2MoO;5, and that the quantity of hydroxid required in titration 
corresponds much more nearly to 48 molecules than to 46 mol- 
ecules for each molecule of phosphorus pentoxid. Owing to the 
occlusion of some molybdic acid the author gives the following 
exact formula as that of the unhcated washed yellow precipitate 
actually obtained in analytical work — (NH4)2HP04.i2.i43Mo0.v 
Attention is also called to the fact that the composition of the 
precipitate is more constant and the results more reliable when 

'' American Chemical Journal, 1902, 28 : 298; 1905, 34 : 204. 



i3. 



■I 



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ESTIMATION OF PHOSPHORIC ACID 



165 



the phosphate solution is added to the molybdic solution than 
the reverse. 

There is a number of other minor well known discoveries in 
this article wdiich need not be mentioned here. The author seems 
to be entirely unaware of the work of the Association of Official 
Agricultural Chemists on this subject. 

The conclusions seem to be applicable to the conditions under 
which the author worked, but criticism might be made that the 
precipitate w^as not sufficiently washed in any of the experiments, 
and further, that the quantity of precipitate is very much larger 
than it is customary to use when working this method, weighing 
as it does almost three grams. The value of all the work de- 
pends on the washing of the yellow precipitate, which, as has been 
said, was incomplete, and no evidence is given to show that im- 
purities could not have been entirely removed. 

146. Estimation of Phosphoric Acid as a Lead Compound. 
— In the volumetric lead method, as described by Wavelet, the 
phosphoric acid is precipitated by the magnesium citrate solu- 
tion as in the uranium method of Joulie, as practiced by the 
French chemists, and the washing of the precipitate and its solu- 
tion of nitric acid are also conducted as in that method." After 
solution in nitric acid, ammonia is added to neutrality and the 
solution is then made acid with acetic. The phosphoric acid is 
precipitated in the acid solution by a standard solution of lead 
nitrate, the precipitate having the formula PoOj.,3PbO. 

The end reaction is determined by ])lacing a drop of the 
titrated mixture on a white greased dish in contact with a drop 
of a five per cent, solution of potassium iodid. When all tlie 
phosphoric acid is precipitated, the least excess of the lead salt 
is revealed by the characteristic yellow precipitate of lead iodid. 

The author of the process claims that the lead phosphate is in- 
soluble in the excess of acetic acid, and that the phosphate itself 
does not give any yellow coloration with potassium iodid. The 
process is quite as exact as the uranium method and the end 
reaction is far sharper ; the standard reagents are easily made 
and preserved.-^ The method described merits, at least, a com- 

'" Repertoire de I'liariiiacie, 1893 [3], 5 : 153. 

'^-^ Revue deChiniie analytique appliqu(^'e, 1893, 1 : 113. 



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AGRICULTURAI. ANAI.YSIS 



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modified 



parative trial with the nraniiini process, but can ni)t be recom- 
mended as exact until further approved by experience. 
The reagents employed have the following composition : 

( 1 ) Disodium phosphate solution containing 10.085 grams per liter 

(2) Sodium acetate " " 50.000 

(3) Lead nitrate " " 40.000 

(4) Potassium iodid " " 50.000 
The titrations should be conducted in the cold. 
147. Water-Soluble Phosphoric Acid. — Glascr has 

the volumetric method of Kalmann and Meissels for the volu- 
metric estimation of water-soluble phosphoric acid in superphos- 
phates so as to avoid the double titration required by the original 
method.-"' If methyl orange be used as an indicator in the orig- 
inal method, the determination does not at once lead to the tri- 
calcium salt, but the liquid still contains, after neutralization, some 
monocalcium phosphate, which is determined by a further titra- 
tion with ])henolphthalein as indicator. In the modified method 
the total ])hos])horic acid is estimated in one o])eration as a tri- 
calcium salt. This is secured by adding, at the proper time, an 
excess of calcium chlorid. Two grams of the superphosphate are 
shaken with water several times according to the American official 
method, and finally, after settling, filtered, and the insoluble resi- 
due washed on the filter until the total volume of the filtrate is a 
quarter of a liter. Of this, 50 cubic centimeters are titrated with 
tenth-normal soda-lye, with addition of two drops of methyl 
orange, until the acid reaction has entirely disappeared. There 
is then added neutral calcium chlorid solution in excess. If 
iron and alumina be present, a slight development of an acid 
reaction is produced of which no account need be made. 
Five drops of the phenolphthalein solution are added and 
the titration continued until the alkaline reaction is noted 
throughout the whole mass. The alkaline reaction soon dis- 
appears and to retain it several tenths cubic centimeters of 
alkali are necessary, and thus an excess is easily used. To get 
very shar]) results it is advisable to place the solutions in a high 
beaker, which is kept in vigorous rotation until the alkaline reac- 
" Chemiker-Zeitung, 1894, 18 : 1533. 



i; i 



ESTIMATION OF PHOSPHORIC ACID 



167 



tion is first established. The burette is quickly read and a few 
tenths more alkali added to be certain that the unit point has not 
been missed. On cloudy days the light may be concentrated by a 
lens, for which a flask filled with clear water conveniently serves. 
Each cubic centimeter of the soda-lye corresponds, in the first ti- 
tration, to 7.1 and in the second to 3.55 milligrams of phosphoric 
acid. 

148. Eslimation of Phosphoric Acid in the Presence of a 
Large Excess of Iron. — The volumetric method given below, due 
to Emmerton, depends upon the precipitation of a phosphomolyb- 
date, of constant composition, in the presence of a large excess 
of iron, as in the analysis of iron and steel and iron ores.^^ The 
molybdenum trioxid obtained is reduced by zinc to MojoO^g. 
The action of permanganate on this compound is shown in the 
following equation : 

5Mo,,Oio+i7(K20Mn,0,)=:z6oMo03-f i7K,0-f34MnO. 

Seventeen molecules of permanganate are equal to 60 mole- 
cules of molybdenum trioxid. The iron or steel is dissolved in 
nitric acid, evaporated to dryness, heated, and redissolved in hy- 
drochloric acid, then treated again with nitric acid and evaporated 
until a clear and concentrated solution is obtained free from hy- 
drochloric acid. 

The solution obtained is diluted to 40 cubic centimeters with 
water and washed into a 400 cubic centimeter flask, making the 
total volume about 75 cubic centimeters. Add strong 
ammonia, shaking after each addition, until the mass sets to a 
thick jelly from the ferric hydroxid. Add a few more cubic 
centimeters of ammonia and shake thoroughly, being sure the 
ammonia is present in excess. Add next nitric acid gradually, 
with shaking, until the precipitate has all dissolved ; add 
enough more nitric acid to make the solution a clear amber color. 
The volume should now be about 250 cubic centimeters. Bring 
the solution to 85° and add at once 40 cubic centimeters of 
m.olybdate solution of the following strength : Dissolve 100 grams 
of molybdic acid in 300 cubic centimeters of strong ammonia and 
100 cubic centimeters of w^ater, and pour the solution into 1250 

'" Blair, Chemical Analysis of Iron, Second Kdition, 1891 : 95. 



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AGRICULTURAL ANALYSIS 



VARIATION OF DUDLEY AND NOYES 



169 



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i i 



cubic centimeters of nitric acid (of 1.20 specific gravity) ; close 
the flask with a rubber stopper, wrap it in a thick cloth, and shake 
violently for five minutes. Collect the precipitate on a filter, using a 
pump, and wash with dilute nitric acid (tHNO-^: 50H2O). If a 
thin film of the precipitate should adhere to the fiask it can be re- 
moved by the ammonia in the next operation. Wash the molyl)- 
date precipitate into a 500 cubic centimeter flask with dilute am- 
monia (iHaN^HoO), using about 30 cubic centimeters. Add 
80 cubic centimeters of hot dilute sulfuric acid ( 1H0SO4 :4H.O) 
and cover the flask with a small funnel. Add 10 grams of 
granulated zinc and heat until rapid action begins, and then 
heat gently for five minutes. The reduction is then complete. 
During the reduction the colors, pink, plum, pale green and dark 
green, are seen in the molybdate solution, the latter color mark- 
ing the end of the reaction. 

To remove the zinc, pour through a large folded filter, wash 
with cold w^ater, and fill up the filter once with cold water. lUit 
little oxidation takes place in this way. A port wine color is 
seen on the filter, but this does not indicate a sufficient oxidation 
to make an error. 

In titrating, the color becomes fainter and finally the solu- 
tion is perfectly colorless and shows a single drop in excess 
of the permanganate. The permanganate solution, for conven- 
ience, is made so that one cubic centimeter is equal to 0.000 r 
gram of phosphorus. With iron its value is one cubic centime- 
ter equals 0.006141 gram of iron ; and one cubic centimeter equals 
0-005574 gram of molybdenum trioxid. 

In the case of iron ores 10 grams are dissolved in hydrochloric 
acid, evaporated to dryness, taken up with hydrochloric acid, 
evaporated to a small bulk and the residual hydrochloric acid ex- 
pelled by heating with nitric acid. The insoluble residue is re- 
moved by filtration and the rest of the process conducted as 
above described. This method of determination is advisable in 
the solution of ores rich in phosphorus, intended for the manu- 
facture of iron or steel where basic phosphoric slag is to be util- 
ized as a by-product. 

149 Variation of Dudley and Noyes.— The method of Em- 



merton for the determination of small quantities of phosphoric 
acid or of phosphorus in the presence of a large excess of iron, 
has been modified by Dudley and Pease,-^ and by Noyes and 
Royse.-' As modified, the method is not intended for fertilizer 
analysis, but the principle on which it rests may some time, with 
proper modifications, find application in fertilizer work. The re- 
duction is accomplished in a jones tube, much simplified, so as 
to render it suitable for common use.-^ The molybdic acid is re- 
duced to a form, or series of forms, corresponding to molybdenum 
sesquioxid, as in the Emmerton method, and subsequently, as in 
that method, titrated by a set solution of potassium permanganate. 
The iron or steel filings, containing phosphorus, are brought 
into solution by means of nitric acid. For this purpose two 
grams of them are placed in a half liter flask together witli 50 
cubic centimeters of nitric acid of 1.18 specific gravity. The 
mixture is boiled for one minute, and 10 cubic centimeters of 
permanganate solution of one and a quarter per cent, added. 
Boil again until the pink color disappears. Ferrous sulfate solu- 
tion is next to be carefully added, shaking meanwhile, until the 
solution clears. Cool to 50° and add eight cubic centimeters of 
ammonia of 0.90 specific gravity, stopper the flask, and shake 
until any precipitate which may form is redissolved. Cool or 
warm, as the case may be, until the solution is as many degrees 
above or below 60° as the molybdic solution is above or below 
27°. Add 60 cubic centimeters of molybdic solution, stopper, 
and shake on a machine or by hand for five minutes.' After 
remaining at rest for five minutes pour into a nine centimeter fil- 
ter of fine texture, and wash with the acid ammonium sulfate 
solution in quantities of from five to 10 cubic centimeters each 
time. The filtrate and washings must be perfectly bright. Con- 
tinue the washings until the filtrate gives no color with hydrogen 
sulfid. 

Dissolve the yellow precipitate with 12 cubic centimeters 

^)f 0.96 ammonia diluted with an equal volume of water, and 

'•'Journal of Analytical and Applied Chemistry, 1893, 7 : 108. 

Journal of the American Chemical Society, 1894, 16 : 224. 
'' Journal of the American Chemical Society, 1895, 17 : 129. 
^^ Blair, Analysis of Iron, Second Edition ,1891 : 99. 



I 



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AGRICULTURAL ANALYSIS 



wash the filter with 100 cubic centimeters of water. F'inally add 
to the filtrate and wash-water 80 cubic centimeters of water 
and 10 of strong sulfuric acid. Pass the mixture through the 
Jones reducing tube and follow it with 200 cubic centimeters of 
water, taking care that no air enter the tube during the opera- 
tions. The solution collected in the flask should be at once 
titrated with potassium permanganate. 

In cases where the content of phosphorus is very high the solu- 
tion of the yellow precipitate is made to a definite volume and 
the reduction and titration performed on an aliquot thereof. 

Solutions Used : ( i ) Nitric Acid. — One part of nitric acid of 
1.42 specific gravity and two parts of water by volume. The 
specific gravity of the mixture is about 1.18. 

(2) Permauii^anate Solution for Oxidizinf^. — Dissolve 12.5 
grams of potassium permanganate in one liter of water. 

(3) ferrous Sulfate. — Fresh crystals not effervesced and free 
from phosphorus. 

(4) Ammonia. — The strong ammonia used should have a 
specific gravity of about 0.90 and the dilute of 0.96 at 15.5°. 

(5) Molybdic Solution. — Dissolve 100 grams of molybdic anhy- 
drid in 400 cubic centimeters of ammonia of 0.96 specific gravity 
and pour the solution slowly, with constant stirring, into one 
liter of nitric acid of about r.20 specific gravity. Heat the mix- 
ture to 45° and add one cubic centimeter of a 10 per cent, solu- 
tion of sodium phosphate, stir vigorously, and allow to stand in 
a warm place for 18 hours. The object of adding the sodium 
phosphate is to remove any substance which may contaminate the 
yellow precipitate. Filter before using. 

(C)) Acid Ammonium Sulfate.— To half a liter of water add 
27.5 cubic centimeters of 0.96 ammonia and 24 cubic centimeters 
of strong sulfuric acid, and make the volume one liter with water. 

(7) Potassium Pcrmmii^^auate for Titration. — Dissolve four 
grams of potassium permanganate in tw^o liters of water, heat 
nearly to boiling for an hour, allow to stand for 18 hours, 
and filter on asbestos felt. The solution must not come in con- 
tact with rubber or other organic matter. The solution may be 
standardized with pure iron (piano wire), with thoroughly air- 






VARIATION OF DUDLEY AND NOYES 



171 



dried ammonium oxalate in solution, with a little dilute sulfuric 
acid and with ammonium ferrous sulfate partly crystallized in 
small crvstals from a slightly acid solution. The crystals should 
be well washed and quickly air-dried in a thin layer. The factors 
111 and i- should be used, respectively, to calculate the iron equiv- 
alent. The phosphorus equivalent is obtained by multiplying 
the iron equivalent by -ii_^=o.oi538. 

Reduction Apparatus.— The reduction of the molybdic acid to 
molybdenum trioxid is accomplished in a tube first proposed by 
Jones. The apparatus is shown in Figure 8. A piece of moder- 




Fig. 8. Jones' Reduction Tube. 

alely heavy glass tubing 35 centimeters long, with an internal 
diameter of two centimeters, is drawn out at the lower end so as 
to pass into the stopper of a fiask. A circular piece of perforated 
platinum or porcelain rests on the constricted portion of the tube 
and this is covered with an asbestos felt. The tube is then nearly 
filled with powdered zinc, which is w^ashed, before using, with 



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172 



AGRICULTURAL ANALYSIS 



dilute sulfuric acid (i :2o). A, B, and C represent different meth- 
ods of filtering the niolyhdic solution. In A a platinum cone is 
placed in the constricted portion of the tube and the asbestos felt 
placed thereon and the tube then filled with the granulated zinc. 
In B there is first inserted a perforated disk, then some very fine 
sand, and this is covered with another disk. In C there is a perfor- 
ated disk which is covered with asbestos felt. The filterin^r ar- 

o 

rangemcnt should be such as to prevent any zinc partidles from 
reaching the flask and yet permitting the filtration to go on with- 
out nuich difficulty. A blank determination is first made by addmg 
to 180 cubic centimeters of water 12 of 0.96 ammonia and 10 of 
strong sulfuric acid. This is poured through the reducing tube 
and followed with 200 cubic centimeters of water, taking care 
that no air enter the apparatus. Hydrogen peroxid is formed if 
air enters. Even after standing for a few moments the tube should 
be washed with dilute sulfuric acid before again using it. The 
filtrate should be titrated with the permanganate solution and the 
amount required deducted from the following amounts obtained 
with the molybdic salt. 

Calculations. — The calculations of the amount of phosphorus 
in a given sample of iron or steel are made according to the fol- 
lowing data:-" In a given case let it be supposed that the per- 
manganate solution is set with a solution of piano wire containing 
99.27 per cent, of pure iron, and it is found that one cubic centi- 
meter of permanganate liquor is equal to 0.003466 gram of me- 
tallic iron. It is found that 90.76 parts of molybdic acid will pro- 
duce the same effect on permanganate as 100 parts of iron. Hence 
one cubic centimeter of permanganate solution is equivalent to 
0.003466X0.9076=0.003145 gram of molybdic acid. In the yel- 
low precipitate formed, in the conditions named for the analysis 
It IS found that the phosphorus is one and nine-tenths per cent, 
of the molybdic acid present. Therefore, one cubic centimeter 
of permanganate liquor is equal to 0.003145X0.019=0.0000597 
gram of phosphorus. If then, for example, in a sample of iron 
or steel eight and six-tenths cubic centimeters of permanganate 
Dudley and Pea«e, Journal of Analytical and Applied Chemistry, 1893, 



112. 



INTERNATIONAL STEEL STANDARDS COMMITTEE 173 

solution, after correction, be f6und necessary to oxidize the molyb- 
dic solution after passing through the Jones reducing tube, the 
amount of phosphorus found is 0.0000597X8.6=0.051 per cent. 
150. Methods of the International Steel Standards Committee.^^ 
—This method was adopted by the committee appointed to con- 
sider all the rapid methods for the determination of phosphorus 
in iron and steel, and was recorded as giving the best methods 
of procedure which are known at present and securing data 
which are of great accuracy if the details of the process are 
carefully observed. The process is conducted as follows: 

From one to two grams of the drillings of iron or steel, accord- 
ing to the phosphorus which they contain, are placed in a 250 
cubic centimeter erlenmeyer flask and covered with 100 cubic 
centimeters of nitric acid of 1.135 specific gravity. The flask is 
covered with a watch-glass and the mixture is heated until the 
solution is complete and the nitric acid is boiled off. Ten cubic 
centimeters of strong potassium permanganate solution are added 
and boiling continued until the pink color has disappeared and 
the manganese dioxid has separated. Afterwards a few drops 
of the solution of sulfurous acid are added and a small crystal of 
ferrous sulfate, or a solution of 0.5 gram of sodium hyposulfite 
in 10 cubic centimeters of water. The addition of these reagents 
is continued at short intervals until the precipitated manganese 
dioxid is dissolved. After boiling for two minutes the flask is 
placed in cool water or allowed to stand until it is cool, and 
then 40 cubic centimeters of dilute ammonia of 0.96 specific 
gravity are added. The precipitated ferric hydrate will redis- 
solve when the liquid is thoroughly mixed. After cooling to 
about room temperature the flask is stoppered and shaken for 
five minutes, either by hand or in a shaking machine. After 
standing for a few minutes, the contents of the flask are poured 
on a filter and washed with acid ammonium sulfate, prepared 
by adding 15 cubic centimeters of strong ammonia to one liter of 
water and 25 cubic centimeters of strong sulfuric acid, until 
two or three cubic centimeters of the wash-water give no reac- 
tion for molybdenum with a drop of ammonium sulfid. Any 
^ Blair, The Chemical Analysis of Iron, 6th Edition, 1906 : 92. 



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174 



AGRICULTURAL ANALYSIS 



1 



adhering ammoiiiuni phosphomolyljdate is dissolved with ammo- 
nia and added to the precipitate in the filter, and the filtrate is 
collected in a 250 cnhic centimeter griffin beaker. The fiask is 
washed with water which is poured uix>n the filter and the filter 
is thoroughly washed until the solution measures about Tx) cubic 
centimeters. To this are added 10 cubic centimeters of strong 
sulfuric acid and the solution is passed through the reductor, 
similar in construction to the jones reduclor already described. 
Care should be exercised to keep the end of the small tube of the 
reductor just bek)w the surface of the licjuid in the fiask. The 
heat which is caused by mixing the strong sulfuric acid with, 
the ammoniacal solution immediately before passing it through 
the reductor is sufficient to insure a comi)lete reduction. The 
other precautions which have already been described to prevent 
the access of air should be observed, and the operations should 
be so continued that the whole reduction occupies about three 
or four minutes. The liquid as it passes through the reductor 
should be bright green in color. Permanganate solution is added 
and the green color disappears. The solution becomes first, 
brown, then pinkish yellow, and ultimately colorless. The ad- 
dition of permanganate is continued drop by drop until the solu- 
tion assumes a faint pink coloration, which remains at least one 
minute. From the reading of the burette the amount of per- 
manganate consumed in the blank determmation, obtained as 
described under the method for standardizing permanganate 
solution, is subtracted and the number of cubic centimeters thus 
obtamed is multiplied by the value of one cubic centimeter in 
terms of phosphorus. This product is multiplied bv 100 and di 
vided by the weight of the sample used and the resulting quotient 
is the percentage of phosphorus in the steel. 

151- Standardization of the Solution of Potassium Permangan- 
ate -This solution is prepared by dissolving two grams of crys- 
tallized potassium permanganate in one liter of distilled water 
and hltcnng through asbestos. For determining its value from 
0.15 to 0.25 gram of clean soft steel wire, in which tlic content 
of iron has been carefully determined, is put in an erlenmever 
flask of 125 cubic centimeters capacity and covered with 30 cubic 







OPERATION OF THE REDUCTOR 



175 



centimeters of distilled water and lo of strong sulfuric acid. 
The flask is covered with a watch-glass and heated untd the solu- 
tion of the wire is complete. A sufficient amount of the strong 
solution of potassium permanganate is added to oxidize the iron 
and destroy the carbonaceous matter, avoiding however any ex- 





, ~ 1 ^Mi. A 44»^i,«^A.if Fic 10 PerniaiiKanate Rurette.^ 

Fig 9 Reductor and Filter Attachment. riR. lu. irci t. 

(Courtesy of A. H. Blair and J. B. Uppincott Co.) 

cess which would cause a precipitate of manganese dioxid. If 
any precipitate is formed it is redissolved by adding a very few 
drops of sulfurous acid and boiling until every trace is removed. 
After cooling 10 cubic centimeters of dilute ammonia arc added 
and the solution passed through a jones reductor. 

152. Operation of the Reductor.— Everything in connection 
with the reductor should be clean and proved to be in good order 
by previous treatment with dilute sulfuric acid and washing with 



? 3 1 



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H 



176 



AGRICULTURAL ANALYSIS 



M- 



distilled water. To this end the flask should be attached to the 
filter pump as shown in the figure. One hundred cubic centi- 
meters of warm dilute sulfuric acid are placed in the funnel b, and 
the stop-cock c opened. When the funnel is almost empty' the 
solution which is to be reduced is transferred thereto. The solu- 
tion siiould be hot, but not boiling. The vessel which held the 
solution should he washed with dilute sulfuric acid, and this 
added to the funnel again when it is nearly empty in such a wav 
as to wash it thoroughly and this should be followed with about 
200 cubic centimeters more of warm dilute sulfuric acid, and ko 
cubic centimeters of hot distilled water. In no case is the funnel 
allowed to become empty, and tlie stop-cock c is closed when 
there is still a little of the wash-water left in the funnel above 
the surface of the zinc. In this way air is prevented from pass- 
ing into the reductor tube, lilank determination is made by 
passing through the reductor a mixture containing 10 cubic 
centimeters of strong phosphoric acid, ro cubic centimeters of 
dilute ammonia, and 50 cubic centimeters of water This is 
preceded and followed by the dilute acid as described above 
Ihe amount of potassium permanganate required to give this 
blank a distinct color is subtracted from the amount required 
to give the same color to each reduced solution. To estimate 
the value of the solution the weight of the iron wire used is 
multiplied by the percentage of the iron in the wire and divided 
by the nuniber of cubic centimeters of potassium permanganate 
m terms o metallic iron. The result is multiplied by the factor 
0.88163 which IS the ratio of molybdic acid to iron and this 
pro uct by 0.0.794 which is the ratio of phosphorus to m^lybSi 
acid, and the result is the value of one cubic centimeter of the 
permanganate solution 11. terms of phosphorus. The formula 
of the reduced molybdic acid is given as Mo,,0„. 

153. Calculating: Results.-To illustrate the method of calcu- 
lating results Blair gives the following example: The weight 

mett'sT. "'"""''' '^ '■'''' ^'■^•" ^^^"'••- 50 cubic centi- 
meters of permanganate to give the required color. A blank 

centimeter of permanganate, so the quantity required by the 



l-;i 



THE SILVER METHOD 



177 



wire is 49.9 cubic centimeters permanganate. The wire con- 
tains 99.87 per cent, of iron. We have then the following 
equation; namely, 0.1745X0.9987^49.9=0.0034923. This shows 
that one cubic centimeter of permanganate is equivalent to that 
quantity expressed as 0.0034923 gram metallic iron. Multiply- 
ing the value in iron by the ratio of molybdic acid to iron, 
namely, 0.88163, and the product by the ratio of phosphorus to 
molybdic acid, namely, 0.01794, the product is found to be 
0.000055238. This indicates that one cubic centimeter of per- 
manganate is equivalent to 0.000055238 gram of phosphorus. If 
the precipitated ammonium phosphomolybdate from two grams 
of steel require 35.5 corrected cubic centimeters, then the per- 
centage of phosphorus in steel is obtained by the following for- 
"^ula: 35-5X0.000055238X100-^2=0.098, which is equivalent 
to the percentage of the phosphorus of the steel. Vnr further 
details of the process the work of Blair, already cited, should 
be consulted. 

154- The Silver Method.— The separation of the phosphoric 
acid by silver according to the method of Perrot has been inves- 
tigated by Spencer, who found the process unreliable.^^ By a 
modification of the process, however, Spencer obtained fairly sat- 
isfactory results. The principle of this method depends on the 
separation of the phosphoric acid by silver carbonate and the sub- 
sequent titration thereof with standard uranium solution after 
the removal of the excess of silver. The operation is conducted 
as follows : The fertilizer is first ignited until all organic matter 
and residual carbon are destroyed. Solution is then accomplished 
by means of nitric acid and the volume completed to a definite 
quantity. To an aliquot part of the slightly acid (nitric) solu- 
tion, after filtration, varying with the su])posed strength of the 
solution so as to contain about 100 milligrams of phosphorus 
pentoxid, freshly prepared silver carbonate is added in excess, 
that is, sufficient to saturate any free acid present and also to 
combine with all the phosphoric acid. Wash thoroughly with 
hot water and then dissolve the mixed phosphate and silver car- 
bonate in nitric acid, and remove the silver from the solution with 

^' Eighth Auuual Report of Purdue University, 1882 : 240. 



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AGRICULTURAL ANALYSIS 



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sodium chlorid. The phosphoric acid is determined in the filtrate 
by means of a standard solution of uranium nitrate in the man- 
ner already described. Spencer found that the separation of 
the phosphoric acid by the silver method was more exact than by 
the Joulie magnesium citrate process. With practice on the part 
of the analyst in determining the end reaction, the process is both 
rapid and accurate. The method is also inexpensive, as both the 
silver and uranium are easily recovered from the waste. 

155. Volumetric Silver Method. — Holleman has proposed a 
modification of the silver method for the volumetric determina- 
tion of phosphoric acid, having for its chief purpose the more ac- 
curate and easy determination of the end reaction, which is con- 
ducted as described below. •^- The reaction which takes place is 
represented by the equation, Na2HP04+3AgN03=Ag3P04+ 
2NaN03-[-HN03. Although silver phosphate is insoluble in 
water, the nitric acid formed holds some of it in solution. To 
])revent this, acetate of soda is added in excess, and thus the whole 
of the phos})horic acid is obtained as a silver salt. The light is 
to be excluded during the determination by wrapping the flask in 
a l)lack cloth to avoid a discoloration of the silver compound. 
\'olhard's reaction for silver is based on the fact that when solu- 
tions of silver and an alkaline thiocyanate are mixed in the pres- 
ence of a ferric salt, silver is precipitated as thiocyanate.'^''* As soon 
as the least excess of thiocyanate is added, brown ferric thio- 
cyanate is formed, and this marks the end point of the solution. 

In a Hask of 200 cubic centimeters capacity are placed 50 cubic 
centimeters of the liquid to be analyzed, which should not contain 
more than two-tenths gram of phosphoric acid. The solution is 
treated with 10 cubic centimeters of a normal solution of sodium 
acetate and afterwards with a slight excess of decinormal silver 
solution, four and five-tenths cubic centimeters for each o.oi 
gram of phosphoric acid. The solution is neutralized with tenth- 
normal sodium hydroxid, the amount required having been pre- 
viously determined by titrating 10 cubic centimeters of the liquid 
to be analyzed, using phenolphthalein as an indicator. Five times 

" Reciieil des Travaux chimiques des Pays-Bas, 1893, 12 : I. 

'■' Liebig's Annalen der Chemie, 1877, 190 : i. 



DESIRABIUTY OF METHODS 



179 



the quantity required for the neutralization of the 10 cubic centi- 
meters is added, less one-half cubic centimeter. By this treatment 
the phosphoric acid in the presence of sodium acetate is completely 
precipitated as silver phosphate. The excess of silver is determined 
by diluting the mixture to 200 cubic centimeters, filtering, and 
titrating 100 cubic centimeters of the filtrate with ammonium thio- 
cyanate, using a ferric salt ( ferric-potassiuni-alum ) as indicator. 
The presence of sulfuric and nitric acids does not interfere with 
the reaction, but, of course, hydrochloric acid nuist be absent. 
Alkalies and alkaline earth metals may be present, but not the 
heavy metals. 

When iron and aluminum are present 100 cubic centimeters of 
the solution are precipitated with 30 cubic centimeters of nor- 
mal sodium acetate, the phosphoric acid is determined in 50 cubic 
centimeters of the filtrate, and the precipitate of iron and alumi- 
num phosphates is ignited and weighed, and its weight nuiltiplied 
by 2.225 ^s added to the phosphoric anhydrid found volumetric- 
ally. If ammonia be present it nuist be removed by boiling, as 
otherwise it afifects the titration with phenol])hthalein. 

For agricultural i)urj)oses this method can have but little value, 
inasmuch as the phosphates to be examined almost always have 
a certain ])roportion of iron and aluminum. Moreover, since the 
amount of these bases has to be determined gravimetrically, there 
would be no- gain in time and no simplification of the processes 
by the use of the volumetric method as proposed. 

TECHNICAL DETERMINATION OF PHOSPHORIC ACID 
156. Desirability of Methods. — In the preceding i)aragraphs, has 
been given a statement of the ])rincipal methods now in use bv 
chemists and others connected with fertilizer control for the 
scientific and agronomic determinations of phosphoric acid, and 
its agricultural value. 

A resume of the important methods, in a form suited to use 
in a factory for preparing ])h()sphatic fertilizers for the market, 
seems desirable. In these factories the chemists have been accus- 
tomed to use their own, or private methods, anrl there has not 
been a general disposition among them to publish their methods 
and experience for the common benefit. For factory processes, 



i ,- 



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AGRICULTURAI. ANALYSIS 



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a method should be not only reasonably accurate, but also simple 
and rapid. It is evident, therefore, that the general principles 
already indicated must underlie any method which would prove 
useful in factory work. The final determination by the technical 
chemist for the purpose of labeling and complying with the laws 
of the various States, should in all cases be conducted by the 
official methods. Albert has made a resume of methods applica- 
ble for factory control, and these are given here for convenience, 
although they are, in many respects, but condensed statements 
of methods already described.^* 

157. Reagents. Molybdate Solution. — One hundred and ten 
grams of pure molybdic acid are dissolved in ammonia of nine- 
tenths specific gravity and diluted with water to one liter. The 
solution is poured into one liter of nitric acid, of one and two- 
tenths specific gravity, and, after standing a few days, filtered. 

Concentrated Ammonium Nitrate Solution. — Seven hundred 
and fifty grams of pure ammonium nitrate are dissolved in water 
and made up to one liter. 

Alai^jicsia Mixture. — Fifty-five grams of magnesium chlorid, 
70 grams of ammonium chlorid and 130 cubic centimeters of am- 
monia of nine-tenths specific gravity are dissolved and diluted with 
water to one liter. 

Two and One-Half Per Cent. Ammonia. — One hundred cubic 
centimeters of ammonia of nine-tenths specific gravity are diluted 
with water to one liter. 

Joulie's Citrate Solution. — Four hundred grams of citric acid 
are dissolved in ammonia of nine-tenths specific gravity and di- 
luted to one liter with ammonia of the same strength. 

IVai^ner's Citrate Sjlution.— One hundred and fifty grams of 
citric acid are exactly neutralized with ammonia, then 10 grams 
of citric acid added and diluted to one liter with water. 

Sodium Acetate Solutio)i. — One hundred grams of crystallized 
sodium acetate are dissolved 111 water, treated with 100 cubic 
centimeters of acetic acid, and diluted to one liter with water. 

Calcium Phosphate Solution. — About to grams of dry, pure 
tribasic calcium phosphate are dissolved in nitric acid and dilu- 
Zeitschrift fiir aiigewandte Chemic, 1891, 4 : 278. 



34 



REAGENTS 



181 



ted with water to one liter. In this solution the phosphoric acid 
is determined gravimetrically by the molybdate or citrate method, 
and the value of the solution marked on the flask containing it. 

Titrated Uranium Solution. — Two hundred and fifty grams of 
uranium nitrate are dissolved in water, 25 grams of sodium ace- 
tate added, and the whole diluted to seven liters. One cubic 
centimeter of this solution corresponds to about 0.005 gram of 
phosphorus pentoxid. In order to determine its exact value pro- 
ceed as follows. Twenty-five cubic centimeters of the calcium 
phosphate solution wdiich, for example, has been found to contain 
0.103 1 7 gram of phosphorus pentoxid, are neutralized in a por- 
celain dish with ammonia, acidified with acetic, treated with 10 
cubic centimeters of sodium acetate solution and warmed. Through 
a burette as much uranium solution is allowed to flow as is neces- 
sary to show in a drop of the solution taken out of the dish, when 
treated with a drop of pure potassium ferrocyanid, a slight brown 
color. In order to be certain, this operation is repeated two or 
three times with new quantities of 25 cubic centimeters of calcium 
phosphate solution. Example : 

Twenty-five cubic centimeters of the calcium phosphate solu- 
tion containing 0.10317 gram of phosphorus pentoxid, gave as a 
mean of three determinations 22^.2 cubic centimeters of the ura- 
nium solution necessary to produce the brown color with potas- 
sium ferrocyanid. Consequently — ^ — ^—^ = 0.00445 gram of 

23'2 

phosphorus pentoxid equivalent to one cubic centimeter of ura- 
nium solution. If, for instance, a quantity of fertilizer weighing 
exactly five grams, requires 10 cubic centimeters of the uranium 
solution for the complete precipitation of its phosphoric acid, 
then the quantity of phosphoric acid contained in the fertilizer 
would be equivalent to 10X0.00445, equivalent to 0.0445 gram of 
phosphorus pentoxid. The fertilizer, therefore, contains 0.89 per 
cent, of phosphorus pentoxid. 

Conduct of the Molybdate Method. — This method rests upon 
the precipitation of the phosphorus pentoxid by a solution of 
ammonium molybdate in nitric acid, solution of the precipitate 
in ammonia, and subsequent precipitation with magnesia. 






4: 



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AGRICUI^TURAIv ANALYSIS 






Manipulation. — Twenty-five or 50 cubic centimeters of a solu- 
tion of the pliosphate which has been made up to a standard vol- 
ume and contains about one-tenth <^ram of phosphorus ])ent- 
oxid, are placed in a beaker together with 100 cubic centimeters 
of the molybdate solution and treated with as much ammonium 
nitrate solution as will be sufficient to p^ive the liquid a content 
of 15 per cent, of ammonium nitrate. The contents of the beaker 
are well mixed and warmed for about 20 minutes at from 60° to 
80.° After coolin^;-, they are filtered and the ])recipitate washed 
on the filter with cold water until a drop of the filtrate saturated 
with ammonia does not become opaque on treatment with am- 
monium oxalate. The filtrate is washed from the filter with 2.5 
per cent, ammonia solution and precipitated slowly and with con- 
stant stirrino;- by the magnesia mixture. After standing- for two 
hours the ammonium magnesium phosphate is separated by filtra- 
tion, washed with 2.5 per cent, ammonia until the filtrate contains 
no more chlorin, and ignited. 

Conduct of the Citrate Method.— The principle of this method 
depends upon the fact that when a sufficient quantity of ammo- 
nium citrate is added to phosphate solutions, iron, alumina, and 
lime are retained in solution when, on the addition of the mag- 
nesia mixture in the presence of free ammonia, the phosi)h()ric 
acid is completely precipitated as ammonium magnesium phos- 
phate. 

Manipulation. —Vrom 10 to 50 cubic centimeters of the solu- 
tion of the phosphate to be determined are treated with 15 
cubic centimeters of the Joulie citrate solution avoiding warm- 
ing. A few pieces of filter pai)er, the ash content of which is 
known, are thrown in and, with stirring, 15 cubic centimeters 
of magnesia mixture slowly added and if necessary also some free 
ammonia. \\y the small pieces of filter paper the collection of 
the precipitate against the sides of the vessel and on the stirring 
rod is prevented and in this way the production of the precipitate 
hastened. After standing from one-half an hour to two hours the 
mixture is filtered, ignited, and weighed. If it be preferred to 
estimate the phosphoric acid by titration, the precipitate is dis- 
solved in a little nitric acid made slightly alkaline with ammonia. 



REAGENTS 



183 



and then acid with acetic and then afterwards titrated with the 
standard uranium solution. 

Conduct of the Uranium Method.— The principle upon which 
this method rests depends upon the fact, that uranium nitrate or 
acetate precipitates uranium phosphate from solutions contain- 
ing phosphoric acid and which contain no other free acid except 
acetic. In the ])resence of ammonium salts the precipitate is 
uranium ammonium phosphate having the formula P04NH4Ur02. 
The smallest excess of soluble uranium salt is at once detected 
by the ordinary treatment with potassium ferrocyanid. 

Manipidation. — In all cases the solution is first made slightly 
alkaline with ammonia and then acid by a few drops of acetic 
so that no free mineral acid may be present. 

( I ) With liquids free of iron : 

If, on the addition of ammonium or sodium acetate, no tur- 
bidity be produced, the liquid is free of iron and alumina. In 
this case from 10 to 50 cubic centimeters of the solution con- 
taining about one-tenth gram of phosphorus pentoxid are treated 
with 10 cubic centimeters of sodium acetate, and afterwards 
with a quantity of uranium solution corresponding, as nearly as 
possible, to its supposed content of phosphorus pentoxid, and 
heated to boiling. From the heated liquid, by means of a glass 
rod, one or two drops are taken and placed upon a porcelain 
])late and one drop of a freshly prepared solution of potassium 
ferrocyanid allowed to flow on it. If no brown color be seen at 
the point of contact of the two drops, additional quantities of the 
uranium solution are added and, after boiling, again tested with 
potassium ferrocyanid until a brown color is distinctly visible. 
The quantity of the uranium solution thus having been deter- 
mined, duplicate analyses can be made and the whole quantity 
of the uranium solution added at once with the exception of the 
last drops which are added as before. 

(2) Solutions containing iron and alumina. 

The solution is treated with the ammonium citrate solution of 
Joulie, the magnesia mixture added slowly, and the precij)itate 
collected on a filter and washed with 2.5 per cent, ammonia. The 
precipitate is then dissolved in nitric acid, made alkaline with 



'I: 



1 84 



AGRICULTURAL ANALYSIS 



PHOSPHATES AND BASIC SLAGS 



i^^5 



ammonia, and then acid with acetic. This sokition is treated 
with 10 cubic centimeters of sodium acetate and titrated with 
uranium, as described in (i). As an alternative method, 200 cubic 
centimeters of the superphosphate solution may be treated with 50 
cubic centimeters of sodium acetate, allowed to stand for some 
time, and filtered through a filter of known ash content. In 50 
cubic centimeters of the filtrate, which correspond to 40 cubic 
centimeters of the original solution, phosphoric acid may be de- 
termined as described above. The precipitate, consisting of iron 
and aluminum phosphates, is washed three times on the filter with 
boiling water, dried, and ignited in a platinum dish. The weight 
of ignited precipitate, diminished by the weight of the ash con- 
tained in the filter and divided by two, gives the quantity of phos- 
phorus pentoxid which it is necessary to add to that obtained by 
titration. 

158. Determination of the Phosphoric Acid in all Phosphates 
and Basic Slag's. 

(i) Total Phosphoric Acid: 

Five grams of the fine phosphate meal, or slag meal, are moist- 
ened in a flask of 500 cubic centimeters content with some water 
and boiled on a sand bath \yith 40 cubic centimeters of hydro- 
chloric acid of from 16^ to 20° Beaume. The boiling is continued 
until only a few cubic centimeters of a thick jelly of silicic acid 
remain. After cooling, some water is added and the phosphate 
shaken until the thick lumps of silica are finely divided. The 
flask is then filled to 500 cubic centimeters and its contents fil- 
tered. Fifty cubic centimeters of the filtrate are mixed with 15 
cubic centimeters of the Joulie solution and treated in the manner 
described with magnesia mixture, precipitated, ignited and 
weighed. The precipitate can also be dissolved and treated with 
uranium solution as described. 

The method used by Oliveri for basic slags mav also be em- 
ployed and it is carried out as indicated in the followinir descrip- 
tion.'^-'' ^ 

A weighed quantity of the slag is reduced to a fine powder. 
To ^wd grams of the sample is added three times its weight of 

" Le Stazioni speriineiitali agrarie italiane, 1891, 20 : 159. 



35 



potassium chlorate and the whole is intimately mixed. The mix- 
ture is then placed in a porcelain dish and hydrochloric acid 
is added, little by little, until the potash salt is completely decom- 
posed. It is evaporated until the mass is dry. The material is 
then treated with fuming nitric acid, and the determination of 
the phosphorus is made by the ordinary gravimetric method. 

By carrying on the operation as described above, a reduction 
of phosphoric acid is avoided, and the presence of an abundant 
quantity of potash prevents the formation of basic iron phosphate 
which is insoluble in nitric acid. 

(2) Citrate-Soluble Phosphoric Acid.— One gram of the basic 
slag or phosphate is placed in a 100 cubic centimeter flask and 
covered with Wagner's acid citrate solution making the total vol- 
ume up to 100 cubic centimeters. With frequent shaking the 
flask is kept at 40° for an hour, or it may be allowed to stand for 
12 hours at room temperature with frequent shaking. In 50 
cubic centimeters of the filtrate from this flask the phosphoric 
acid is determined by the magnesia mixture as described. Since, 
in the present case, the precipitate of ammonium magnesium 
phosphate contains some silicic acid it can not be directly ignited 
but must be treated in the following manner: The precipitate 
and the filter are thrown into a porcelain dish, the filter paper 
torn up into shreds with a glass rod, the precipitate dissolved 
in nitric acid, neutralized with ammonia, acidified with acetic, 
and treated with uranium solution. The phosphoric acid may 
also be estimated by the gravimetric method by dissolving the 
])fecipitfite again in hydrochloric or nitric acid, evaporating to 
dryness, and drying for one hour at from 110° to 120°, dissolv- 
ing again in hydrochloric acid, filtering, and washing the precip- 
itate well. The filtrate, which is now free from silica, can be 
treated with Joulie's solution, precipitated with magnesia mixture, 
the precipitate washed, ignited, and weighed as described. The 
molybdate method is preferred in the estimation of citrate-solu- 
ble phosphoric acid, especially in slags. For this purpose 50 cubic 
centimeters of the filtrate from the solution of one gram of slag 
in 100 cubic centimeters of Wagner's citrate li(|uid are treated 
with 100 cubic centimeters of molybdenum solution and 30 cubic 



r 



n 
m 



11 



I 



i 



S 1 



1 

II 



1 86 



AGKICUI^TURAL ANALYSIS 



FRKE ACID IN PH0SPHATE:S 



187 



centimeters of amnioniuni nitrate solution, warmed for 20 minutes 
at 80°, filtered after cooling, and the yellow i)recipitate washed 
with cold water. The water will p^radually dissolve all the silicic 
acid from the yellow |)recipitate and carry it into the filtrate. The 
yellow precipitate is then dissolved in 2.5 per cent. li(|ui(l ammonia 
and i)recipitated with ma^^nesia mixture and the ])recipitate 
washed, ij^nited and weighed in the way described. 

159. Determination of Phosphoric Acid in Superphosphates. 
— (i) Citrate-Soluble Phosphoric Acid. — Five grams of the su- 
perphosphate are rubbed with 100 cubic centimeters of Wagner's 
acid citrate solution in a mortar and washed into a flask of 500 
cubic centimeters content and diluted to 500 cubic centimeters 
with water. With frecpient shaking, the ilask is allowed to 
stand for 12 hours, after which its contents are filtered. Fifty 
cubic centimeters of the filtrate are treated with 10 cubic centi- 
meters of the Joulie solution and 15 cubic centimeters of the mag- 
nesia mixture and, if necessary, made distinctly alkaline with am- 
monia, vigorously stirred, and, after two hours, filtered. The 
precii)itate is washed, ignited, and weighed as described, or titrat- 
ed, after solution in nitric acid and the addition of sodium ace- 
tate, with uranium solution. Fxample : The weighed precipi- 
tate has 0.1272 gram MgJ\.()-, then the i)h()S])hate contains 
1 2.72X2X0.64= ir).2<S per cent, of citrate-soluble P.O,,. 

(2) Watcr-Solublc Phosphoric Acid. — Twenty grams of super- 
phosphate are rubbed in a mortar and washed into a flask of one 
liter content and made up to the mark with water. After two 
hours digestion with frequent shaking, the contents of the flask 
are filtered through a folded filter. Twenty-five cubic centime- 
ters of the filtrate e(|uivalent to 0.5 gram of the substance are 
precipitated with magnesia mixture, the precipitate filtered, 
washed, ignited, and weighed, or the moist filtrate may be dissolved 
upon the filter with a little nitric acid, treated with .sodium acetate 
and titrated, as described, with uranium solution. 

Examj)le: 14.5 cubic centimeters of the uranium .solution are re- 
quired for the precipitate from 25 cubic centimeters of the orig- 
inal solution=:o.5 gram superphosphate; it contains then 14.5X 



0.00445=0.0645 gram P,0,, Consequently the superphosphate 
contains 12.90 per cent, of water-soluble PgO^. 

Total Phosphoric Acid.— Tv^cnty grams of the superj^hosphate 
are boiled with 50 cubic centimeters of hydrochloric acid of from 
i(f to 18° Beaume for about to minutes and, after cooling, made 
up to one liter with water and filtered. Twenty-five cubic centi- 
meters of the filtrate are treated with 10 cubic centimeters of 
Joulie's citrate solution, a few pieces of filter paper thrown in. 
K cubic centimeters of magnesia mixture added, and the 
whole thoroughly stirred. After standing two hours the contents 
of the flask are filtered, the precipitate is washed with dilute 
ammonia, and the filter and the precipitate are placed in a platinum 
crucible. The crucible is heated slowly until the moisture is driv- 
en off and the filter burned. Then the temperature is gradually 
raised to a white heat. The residue is cooled and weighed. 

Example: The precipitate weighs, after the subtraction of the 
filter ash, 0.1390 gram; then the superphosphate contains 13.90 
X 2X0.64= 1779 P^^ cent, phosphoric acid. 

160. Determination of Free Acid in Phosphates for Technical 
Purposes. — A speedy and approximately accurate •method of 
determining free ])h().sphoric acid in su])erphosphates is useful m 
technical work, and for this purpose Gerhardt has j^roposed the 
following process.-'" There are valid objections to both the meth- 
ods in common use. When the free acid is extracted with 
water and the acidity of the extract determined by titration with 
an alkali, the end reaction is obscured bv the separation of acid 
calcium phosphate, CaTTPC),. On the other hand, when absolute 
alcohol is used to dissolve the acid, the separation is not exact 
because of the water content of the sample, and drying the sample 
would cause a decomposition and the formation of new com- 
pounds of the free phosphoric acid. The principle of the fol- 
lowing process is based on the addition of an excess of calcium 
carbonate to the sample and the subsequent determination of the 
undecomposed portion. 

When pure i)hos])horic acid is shaken with calcium carbonate 
the following reaction takes place : 

2H3PO,H-CaC03=CO,+H,0+CaH, ( PO J ^ 

^ Chemiker-Zeituiig, 1905, 29 : 178. 



'<■ » 



f «a 



\ii 



r) 



; if H 



1 88 



AGRICULTURAL ANALYSIS 



ostersetzer's method 



189 



The sulfates of iron and aluminum disturb the accuracy of the 
reaction, since they also react with carbonates. Inasmuch as the 
mineral phosphates entering the factory have been examined for 
iron and alumina, the maj^^nitude of this disturbance can be as- 
certained and due allowance made therefor, or the iron may be 
thrown out previous to the determination by potassium ferrocya- 
nid. The process is conducted as follows : 

Twenty grams of the sample are shaken for half an hour in a 
liter flask with water, and one gram of ferrocyanid of potash dis- 
solved in water added thereto, the flask filled to the mark, shaken, 
and the contents poured on a filter. To 100 cubic centimeters of 
the filtrate a known weight of calcium carbonate is added, stirred 
for half an hour, the undecomposed carbonate separated by filtra- 
tion, washed with a small quantity of water, dried, ignited gently 
and weighed. The ([uantity of calcium carbonate thus determined 
deducted from the whole amount used, represents the quantity de- 
composed by the free acids and the iron and aluminum compounds 
above noted. The constant error, due to the last named source, 
is applied as a correction and the quantity of free acid thus ap- 
proximately' determined. 

The carbon dioxid contained in the residue above mentioned 
is determined more rapidly and with greater precision by decom- 
posing it with an acid and weighing or measuring the evolved 



gas. 



The carbonate remaining in the residue may also be determined 
by titration as follows: The residue is placed in a flask of 200 
cubic centimeters capacity and decomposed with 25 cubic centime- 
ters of normal hydrochloric acid, filled to the mark, shaken and the 
contents poured through a dry filter. One hundred cubic centi- 
meters of the filtrate are titrated with half-normal soda-lye, using 
methyl orange as indicator. The correction for iron and aluminum 
must again be made, since any iron and aluminum phosphate which 
is found with the residue of calcium carbonate decomposes cor- 
responding cjuantities of the hydrochloric acid. Since the fresh 
superphosphate always contains some free sulfuric acid, it is ad- 
visable to report the result as degree of acidity, comprising therein 
the free phosphoric acid, the free sulfuric acid and all other com- 



pounds of an acid character which react with calcium carbonate 

to form carbon dioxid. , , • 

When an aqueous solution of CaH,(PO,), and free phosphoric 
acid is titrated with an alkali in the presence of methyl orange, 
no precipitate is produced ; and, therefore, the precipitate in the 
above method, ascribed to the formation of CaHPO,, is rather to 
be accredited to the production of a phosphate of iron or alumina. 
The alcohol method of extraction is not, therefore, as Gerhardt 
has supposed, inapplicable because superphosphate may go into 
solution, since this does not interfere with the reaction when 
methyl orange is used as indicator, but it is to be rejected for 
other reasons. The errors, however, due to iron and alumina may 
amount to as much as one or two per cent, and are not constant. 
Gerhardt maintains in a later publication that Zockler is mis- 
taken respecting the non-formation of CaHPO, and regards his 
method as above described as satisfactor>', especially when the 
calcium carbonate is titrated instead of ignited.^^ 

161. Ostersetzer's Method.— The ''free" acid in superphos- 
phates may consist of several kinds, free phosphoric acid, free 
sulfuric acid and acid phosphates which react as free acid. An 
indicator that may be used in a purely technical way to indicate 
the proportion of such free acid to the total acid present is aliz- 
arin sulfonic acid.^« The determination of total free acidity is 

made as follows : 

Dissolve 10 grams of superphosphate in 400 cubic centimeters 
of water in a 500 cubic centimeter flask. Shake for the usual 
time and add four cubic centimeters of a solution containing two 
and a half grams of alizarin sodium sulfonate in 500 cubic centi- 
meters of water. Complete the volume to the mark, filter, titrate 
50 cubic centimeters of the filtrate, representing one gram of the 
sample, with half-normal sodium hydroxid solution to transi- 
tion between yellow and brown, comparing with an equal volume 
of the original solution to better distinguish the changed color. 
The free acidity is calculated from the data obtained and com- 
pared with the total acidity determined in the usual way. 

37 Zockler, Chemiker-Zeitun^^ 1905, 29 : 226, 338. 

3» Chemiker-Zeitung, 1905, 29 : 276. 

=»» Chemical News, 1905, 91 : 215. 



1^1 



r 



i'i 



' i 



I 



J90 



AGRICUU'URAI^ ANALYSIS 



USES OF BASIC SLAG 



191 



i 



BASIC PHOSPHATIC SLAGS 

162. Uses of Basic Slag. — Tlie importance of basic Bessemer 
slag, the residue of the process of manufacturing steel by the basic 
process from ores rich in ])hosphoriis,isevery\vhere acknowledged. 
The use of this material in the I'nited vStates has not been very ex- 
tensive, chiefly for the reason that practically none of it is pro- 
duced in this country, ste^d not being made from phosphatic 
ores, it is, however, made in very large (juantities in Europe, 
and it is stated that over 2,cxx),ooo tons of it are used annually 
in Germany alone for manurial purposes. 

Leavens has given the following reasons for believing that 
basic slag is a superior (piality of i)hosphatic fertilizer:'*'* 

I. 'J'he phosphoric acid in basic slag is in a form which can 
not revert or go back to more insoluble forms when mixed with 
the soil as is the tendency with all su])erphosphates. 

II. The phosphoric acid in basic slag is not washed from the 
soil by the heavy rains and leached awav in the drainage waters 
as is the case with many other phosphates. 

III. Since the phosphoric acid in basic slag never wastes after 
application to the soil, it follows that basic slag may be applied 
at any tune, either fall, spring, summer, or even in winter without 
danger of loss. 

IV. in addition to its high content of phosphoric acid, the 
large amount of lime in basic slag greatly adds to its value. In- 
stead of having a souring el'fect upon the land, as do superphos- 
phates, basic slag on account of its strong alkaline reaction sweet- 
ens acid soils and restores them to a productive condition. 

The lime also ])ossesses the valuable property of making avail- 
able the potash already in the soil and has a similar effect on^ 
crude forms of organic nitrogen. In addition to the chemical 
effects already mentioned, lime greatly improves the physical 
quality of the land, loosening up compact clav soils, thus 'mak- 
ing them more permeable, and compacting light sandv soils ren- 
dering them more retentive of moisture and plant food. 

V. i^asic slag also contains a considerable amount of magnesia 
which IS extremely valuable in changing crude forms of plant 

*<* Basic Slag and its Uses, 1906 : 5. 



foods in the soil into forms which the plant may take up readily. 
So powerful is its action in this direction that it is often spoken 
of as "a chemical plow." 

VI. The large amount of iron in the basic slag should not be 
overlooked. "Iron," says Prof. Sorauer, in his excellent treatise 
on the physiology of plants, '^is necessary in the building of chloro- 
phyll," the substance that gives the green color to all foliage 
"As it is the function of chlorophyll to form new plastic material 
under the influence of the sunlight, it is natural that the absence 
of iron, which is shown by the paleness of the leaves, should cause 
a cessation of assimilation." 

This accounts for the deep green color and splendid healthy 
condition of the foliage of the plants and trees fertilized with 
basic slag. 

VII. In addition to all of the above, basic slag commends itself 
strongly on account of the high degree of availability to plants 
possessed by its phosphoric acid. While little or none of its 
phosphoric acid is soluble in pure distilled water, it is soluble 
in the secretions of the plant roots which feed upon it readily. 
Experiments indicate that the total i)hosphoric acid of basic 
slag is practically as effective as the available phosphoric acid 
of acid phosphate. ^^ 

It should be borne in mind that this high degree of availability 
is not due to any treatment of the basic slag with sulfuric 
acid. There is a marked reaction all over the country against using 
acidulated fertilizers, as their continued use under improper con- 
ditions has rendered many thousands of acres of valuable land 

infertile. 

The average total results show that insoluble phosphoric acid, 
that is phosphates which have not been treated or dissolved in 
sulfuric acid (oil of vitriol), have more pounds of crop, both 
straw and marketable grain, than the phosphoric acid in the 
soluble and reverted forms; that is, in phosphates which have 
"been dissolved in sulfuric acid.*'- 

VIII. The comparative low cost of basic slag with resulting 

*i Ohio vState Agricultural Experiment Station, Bulletin 100, 1899 : 137. 
« Maryland Agricultural Experiment Station, Bulletin 68, 1900 : 28. 



i, i< 



I 






192 



AGRICULTURAL ANALYSIS 



economy in crop production, is a matter that should appeal to 
every practical farmer. 

Slag- phosphate plots produced a greater }ield and at a less 
cost than the average of the soluble phosphoric acid plots and 
the bone meal plots. All yields were produced at less cost with 
slag phosphates than with bone meal."*^ 

IX. Whije basic slag generally should not be mixed with mate- 
rials containing nitrogen in organic forms such as dried blood, 
ground bone, dried fish or tankage, many highly desirable and 
splendid combinations of it with nitrate of soda and potash salts 
may be made. 

By varying the amount of nitrate of soda and potash salts mixed 
with the slag, fertilizers adapted for use on all of our leading 
crops may be prepared. 

Wheeler states that basic slag is an effective source of phos- 
phoric acid for use upon all kinds of soils, and on account of 
its lime it is of special promise in the reclamation of exhausted 
acid soils, particularly such as are rich in organic matter, like 
many marsh or muck soils.'** 

Basic slag has been found useful for peaches, apples, grapes, 
oranges, and fruits in general, and for all the cereals. It has 
also proved very beneficial to clover, alfalfa, and the grasses; in 
fact, all kinds of crops which are benefitted by phosphatic fertil- 
izers respond more readily to the fertilizer when in the shape of 
basic slag. Since it is quite likely that it may come into much 
more general use in this country, a detailed study of the methods 
of determining its value is advisable. 

163. History and Manufacture.— The basic process for the man- 
ufacture of Bessemer steel is known in Europe as the Thomas 
or Thomas and Gilchrist process, and the slags rich in phosphate, 
one of the waste products of the process, are known by the 
same name. In this country all the phosphatic slags which have 
been made in the manufacture of steel have been obtained work- 
ing chiefly under the patents of Reese, and, when prepared for the 
market, are known as odorless phosphate. The only places where 

Maryland Agricultural Experiment Station, Bulletin 68, 1900 : 28, 29. 

U. S. Deparlnient of Agriculture, Farmers' Bulletin 77, 1905 : 18. 



43 



44 



)i 



PROCESS OF MANUFACTURE I93 

these slags have been made in this country are Pottstown, Penn- 
sylvania and Troy, New York. Comparatively small quantities 
have been manufacttired and the industry has not assumed any 
commercial importance. In Europe they are extensively manu- 
factured in England, France and Germany, and their use for 
agricultural purposes has increased until it is quite equal to that 
of superphosphates. 

The quantity of basic slag manufactured in Germany in 1893 
was 750,000 tons; in England 160,000; in France 115,000, making 
the total production of central Europe about 1,000,000, a quantity 
sufficient to fertilize nearly 5,000,000 acres. During the year 
1907 it is estimated that German agriculture made use of from 
1,500,000 to 1,600,000 tons of basic phosphate slags. The total 
output of basic slag is undoubtedly not far from 2,000,000 tons. 
The total production of basic slag is therefore approximately 
cne-half of that of crude phosphates. 

The following table in metric terms shows the estimated pro- 
duction of crude phosphates for the whole world for 1906 and 
1907 :^^ 

' 1907 1906 

United States 1,917,000 2,052,000 

Tunis 1 ,040,000 758,000 

Algeria 325,000 302,000 

South Sea Islands 300,000 250,000 

France 375,000 425,000 

Belgium 180,000 155,000 

All other places 100,000 100,000 

4,237,000 4,o42,(X)o 

164. Process of Manufacture. — The principle of the process 
depends upon the arrangement of the furnaces, by means of 
which the phosphoric acid in the iron ore or pig iron is caused to 
combine with the lime, which is used as a flux in the converters 
A general outline of the process is as follows: 

The pigs, which contain from two to four per cent, of phos- 
phorus, are melted and introduced into a Bessemer converter lined 
with dolomite powder cemented with coal-tar, into which has 
previously been placed a certain quantity of freshly burned lime. 

*^ Der Saaten-, Diinger-und Futtermarkt, 1908, No. 7 : 205. 
7 



J 



t : 



i 'i 






194 



AGRICULTURAL ANALYSIS 



11 



For an average content of three per cent, of phosphorus in the 
pig iron, from 15 to 20 pounds of Hme are used for each 100 
pounds of pig iron. As soon as the melted pig iron has been 
rntroduced into the converter, the air-blast is started, the con- 
verter placed in an upright position, and the purification of the 
mass begins. The manganese in the iron is converted into oxid, 
the silicon into silica, the carbon into carbon dioxid and oxid, 
and the phosphorus into phosphoric acid. 

By reason of the oxidation processes, the whole mass suffers a 
rise of temperature amounting in all to about 700° above the tem- 
perature of the melted iron. At this temperature the lime which 
has been added, melts and, in this melted state, combines with the 
phosphoric acid, and the li(iui(l mass floats upon the top of the 
metallic portion, which has by this process been converted into 

steel. 

As soon as the process, which occupies only about 15 min- 
utes, is completed, the fused slag is poured off into molds, al- 
lowed to cool, broken up, and ground to a fine powder. For each 
five tons of steel which are made in this w^ay, about one ton of 
basic slag is produced. 

In another i)rocess, in order to make a slag richer in phos- 
l'>horic acid, a lime is employed which contains a considerable 
percentage of phosphate. Although the slag thus ])ro(luced is 
richer in phosphoric acid, it is doubtful whether it is any more 
available for plant growth than that made in the usual way with 
lime free from phosphoric acid. Tn other words, when a basic 
slag is made with a lime free from phosphoric acid, nearly the 
whole of the phosphoric acid is combined as tetrabasic calcium 
phosphate. On the other hand, when the lime employed con- 
tains some of the ordinary mineral phosphate, the basic slag pro- 
duced becomes a mixture of this mineral phosphate with the 
tetracalcium salt. The mineral phosphate is probably not ren- 
dered any more available than it was before. 

It is easily seen from the above outline of the process of man- 
ufacture that basic slags may have a very widely divergent com- 
position. When made from pig iron poor in phosphorus, the slag 
will have a large excess of uncombincd lime and consequently the 



TETRACALCIUM PHOSPHATE 



195 



content of phosphoric acid will be low. When made from pigs 
rich in phosphorus there may be a comparative deficiency of iron 
in the slag, and in this case the content of tetrabasic calcium phos- 
phate would be unusually high. 

It is found also that the content of iron in the slag varies 
widely. Tn general, the greater the content of iron the harder 
the slag and the more difficult to grind. If the pig iron contain 
sulfur, as is often the case, this sulfur is found also in the slag in 
combination with the lime, either as a sulfid or sulfate. 

No certain formula can therefore be assigned to basic slags and 
the availability of each one must be judged by its chemical com- 
position. 

165. Composition of Slag Phosphate. — The slags produced by the 
method above outlmed may be amorphous or crystalline. When 
large masses are slowly cooled the interior often discloses a crys- 
talline composition. In some samples analyzed in the labora- 
tory of the Division of Chemistry the crystals were found to be 
of two forms, viz., acicular and tabular.^'' They had the follow- 
ing composition : 

Calculated per cents, as 

FcaO.i. AI2O3. MgO. VoO'.'. PaOf.- SiOo. 

20.98 3.71 0.49 0.18 27.06 4.96 

9.64 0.91 0.08 ... 33.92 1.75 

These data show that the two sets of crystals belong to two 
distinct mineral forms. The presence of vanadium in one of the 
samples is worthy of remark, and leads to the suggestion that in 
the slags made of phosphoriferous pigs may be found any of the 
rare metals which may exist in the ores from which the pigs were 
made. The amorphous portions may have a widely varying com- 
position and consequent variable content of phosphoric acid. In 
all good slags, however, wdiether in crystalline form or as amor- 
phous powder, the lime and phosphoric acid will be found com- 
bined as tetracalcium phosphate (Ca^PoO,,). 

166. Molecular Structure of Tetracalcium Phosphate. — Several 
theories liave been advanced in respect of the atomic arrange- 
ment of the elements contained in a molecule of tetracalcium 
phosphate. It must be confessed that so little is known concern- 

** Journal of Analytical and Applied Chemistry, 1891, 5 : 685. 



CaO. 



Acicular crystals 42.69 

Tabular crystals 53-6i 









196 



AGRICULTURAIv ANALYSIS 



1 



ing the reactions of this body as to make theories of its constitu- 
tion largely visionary. But the existence in definite crystalline 
form of this salt shows that it is not merely an intimate mechan- 
ical mixture, but a true molecular form. As a type of the sup- 
posed arrangement of its particles, the graphic formula proposed 
by Kormann may be consulted ; viz., 

O— Ca r 

/ 

PO— o. 

0/ 



O 



PO— o 

\ 



>Ca 



O— Ca- 



The crystals of this salt, as may be seen by inspection of the 
analytical data, contain other bodies than calcium, oxygen and 
phosphorus. It would be of interest to push the investigation 
of their constitution further and see if crystals of pure tetracal- 
cium phosphate could be obtained, and under what conditions 
they would be contaminated by other metallic oxids. Usually, 
by the color of the crystals, it will be easy to determine some- 
thing of the nature, if not the extent, of the contamination. 

167. Solubility of Phosphatic Slags. — The high agricultural 
value of basic slags led to an early study of their solubility in. 
ammonium citrate, citric acid, and other organic solutions. Even 
finely ground mineral phosphates and bones are soluble to some 
extent in ammonium citrate, as was pointed out as long ago as 
1882.*" The most common solvents for basic slags are 
ammonium citrate and citric acid. The ammonium citrate should 
be the same as that used for the determination of reverted phos- 
phoric acid and the citric acid solution commonly used contains 
five grams in a hundred cubic centimeters. The slags of dif- 
ferent origin and even of different age vary greatly in respect of 
the quantity of soluble matter they contain. It is believed, how- 
ever, that a very fair idea of the agricultural value of a slag 

*' Wiley, Journal of Analytical and Applied Chemistry, 1889, 3 : 413. 



11 



SOLUTION OF PHOSPHATIC SLAGS 



197 



may be obtained by determining its degree of solubility in one of 
the menstrua named. 

168. Separation by Sifting.— The relative availability of a slag, 
as in the case of a mineral phosphate, is determined very largely 
by the percentage of fine material it contains. Sieves of varying 
apertures are used to determine this percentage. A one-half 
millimeter or a one-quarter millimeter circular aperture is best, 
and the percentage of the total material passing through is deter- 
mined. A method used in Germany consists in sifting the slag in 
a sieve 20 centimeters in diameter, the meshes of which are from 
0.14 to 0.17 millimeter square and which measure diagonally from 
0.22 to 0.24 millimeter. 

169. Solution of Phosphatic Slags. — Sulfuric acid has been, 
found to be an excellent solvent for basic slags preparatory to the 
determination of total phosphoric acid. There is, however, no 
unanimity of opinion concerning the best method or means of 
solution. Aqua regia and nitric acid are objected to because they 
may convert any phosphorus in combination with the iron into 
phosphoric acid and thus increase the quantity present.*^ But 
iron phosphid is seldom found in slags, and therefore this objec- 
tion is not always tenable. Sulfuric acid has also been deemed 
objectionable because the gypsum separated is likely to carry 
with it some of the other substances to be determined. 

Hydrochloric acid is also excluded by some from the list of sol- 
vents because it dissolves so many of the foreign elements in the 
slag and thus tends to complicate the subsequent determinations, 
especially of magnesia. Besides, a hydrochloric acid solution is 
not suited to the use of the citrate method fomierly much em- 
ployed m the determination of total phosphoric acid. When 
hydrochloric acid is used, moreover, the dissolved silica must be 
removed and thus the time required for making a phosphoric 
acid determination is much increased. 

If the sample be sufficiently fine the occlusion of undissolved 
phosphate particles by the gypsum formed when sulfuric acid is 
used is not to be feared, and the disturbance of volume by the 
gypsum is nearly constant and can be allowed for. When 

^ von Reis, Zeitschrift fiir angewandte Chemie, 1888, 1 : 354. 






. n 



n 



I 



i 
I 



\ 



I 



' I 






198 



AGRICULTURAL ANALYSIS 



UALLK MKTHOD FOR BASIC SLAG 



199 



five ^rams of sla^ are used the mean volume of gypsum in the 
solution is about two cubic centimeters. 

170, Estimation of Total Acid.— In the determination of total 
phosphoric acid in a slag, 25 cubic centimeters of the strongest 
sulfuric acid are placed in an erlenmeyer having a wide neck, 
and with careful shaking five grams of the fine slag meal grad- 
ually added. The flask is heated over a naked flame until solu- 
tion is complete. When the mass is cold it is washed into a quar- 
ter liter flask ; again allowed to cool, filled with w^ater to the mark, 
and two cubic centimeters of water, corresponding to the volume 
of gypsum undissolved, are added, well mixed, and filtered. Tn 
50 cubic centimeters of the filtrate, the phosphoric acid is deter- 
ininecl by either the molybdate or citrate methods already de- 
scribed. 

171. Alternate Method. — The following method may also be 
used : Ten grams of the substance are heated with 50 cubic cen- 
timeters of concentrated sulfuric acid until white va])ors have 
been evolved for some time. The 0])eration lasts for about 15 
nunutes and can be carried on in a half-liter flask or in a por- 
celain dish. Without regarding the undissolved material, the 
volume of the licjuid is now made u]) to half a liter and filtered. 
The filtered li(|uid becomes turbid after some time through the 
separation of calcium sulfate, but this turbidity should not be 
regarded. To 50 cubic centimeters of the solution, correspond- 
ing to one gram of substance, 20 cubic centimeters of citric acid 
(500 grams citric acid to the liter) are added, and it is after- 
wards nearly neutralized by the addition of 10 ])er cent, am- 
monia and the li(|ui(l. which is warmed by this o])eration, cooled. 
There are added 25 cubic centimeters of the ordinary magnesium 
chlorid mixture and the solution stirred until turbidity is pro- 
duced, one-third of its volume of 10 i)er cent, ammonia added, 
and again stirred for about a minute to ])romote precipitation. 

Instead of the addition of the citric acid and ammonia, am- 
monium citrate ])rej)are(l as follows may be added: Fifteen hun- 
dred grams of citric acid are dissolved with water, made up to 
three liters, five liters of 24 per cent, ammonia and seven liters 



V 



of water added. The rest of the operation is carried on in the 

usual manner. 

172. Halle Method for Basic Slag.— The total phosphoric acid 
is estunated at the Halle Station by the following process :^« 

Ten grams of the substance are moistened in a porcelain dish 
with a few drops of water and about five cubic centimeters of a 
one to one solution of sulfuric acid added, and after the mass has. 
hardened, which takes place very soon, 50 cubic centimeters of 
concentrated sulfuric acid are added and stirred with a glass rod 
until evenly distributed throughout the whole mass. In stir- 
ring this mixture the greatest care must be taken, otherwise some 
of the substance will remain attached to the sides of the dish, 
which during later heating would cause loss through spurting. 
The complete solution takes place after a few hours heating on 
a sand-bath. During the codling, the jelly-like mass must be 
stirred with a glass rod, and after it is cool, by means of a wash- 
ing bottle, gently along the sides of the dish, water is added, and 
when the mixture becomes hot it is again cooled and washed 
into a half-liter flask, which is made up to the mark at a tem- 
perature of 1 7°. 5 and filtered. Wlien the acid filtrate stands for 
some time there is often a separaticm of gypsum that, however, 
does not in any way influence the subsequent analysis, which is 
made in the usual manner. 

Fifty cubic centimeters of the filtrate, representing one gram 
of the original substance, are placed in an erlenmeyer. In the 
case of double superi)hosphates, which often contain large quan- 
tities of pyrophosphates, 25 cubic centimeters of the filtrate just 
obtained, equivalent to 0.5 gram of the substance, are diluted with 
75 cubic centimeters of water, 10 cubic centimeters of nitric acid 
of 1.42 specific gravity added, and heated on a sand-bath to con- 
vert the pyro- into orthophosphates. The heating should be con- 
tinued until the liquid is reduced to its original volume of 25. 
cubic centimeters. The strongly acid lif|uid is saturated with 
ammonia and with the addition of a drop of rosolic acid as an 
indicator, again acidified wath nitric acid, and treated as with 
superphosphates. 

♦» Bieler und vSchneidewind, Die agrikuUur-cheinische Versuchsstatioti 
HaUe, a/S. ihre Einrichtung und Thatigkeit, 1892 : 6r. 



11 
I i 

i 
I 



<l 



it 



II 



200 



AGRICULTUKAI^ ANALYSIS 



1 






!l 



173. Dutch Method for Basic Slag. — Heat 10 granis of the 
sample with 50 cubic centimeters of sulfuric acid (1.84 specific 
gravity) till white vapors are evolved, shaking or stirring con- 
stantly. After cooling, make the fluid up to 500 cubic centi- 
meters with water, taking no account of the undissolved sub- 
stance. Filter, and to 50 cubic centimeters of the filtrate add 
100 cubic centimeters of the an-wnoniacal citrate solution, and 
after cooling, 25 cubic centimeters of magnesia mixture. Stir or 
shake for a sufficient time. After the lapse of two hours the 
precipitate is to be separated by filtration and treated in the usual 
manner. 

174. Estimation of Citrate-Soluble Phosphoric Acid in Basic 
Slag. — Experience has shown that the manurial value of basic 
slags does not depend alone on their content of phosphoric acid. 
Slags may contain tri- as well as tetracalcium phosphate, and 
even this latter salt may exist in states of differing availability. In 
determining the availability of basic slag for manurial purposes, 
its solubility in ammonium citrate is considered the best stand- 
ard. But this solubility will evidently be influenced by the basicity 
of the sample or, in other words, by the quantity of lime present. 
A slag rich in calcium oxid would deport itself differently with 
a given ammonium citrate solution from one in which the lime 
had been chiefly converted into carbonate. If possible, therefore, 
all samples should be reduced to the same state of basicity before 
the action of any given solvent is determined. 

Wagner proposes to neutralize the basicity of a slag in the 
following manner -/"^ Five grams of the slag are placed in a half- 
liter flask, which is then filled up to the mark with a one per cent, 
solution of citric acid and placed for half an hour in a rotating 
shaker. After filtering, 50 cubic centimeters are titrated with a 
standard soda solution, using phenolphthalein as indicator. This 
' gives the quantity of citric acid necessary to neutralize the slag. 
To a second portion of five grams of the sample in a half -liter 
flask are added 200 cubic centimeters of water and enough five 
per cent, citric acid solution to neutralize the lime, and then 200 
cubic centimeters of acid ammonium citrate made as indicated 

*^ Cliemiker Zcitung, 1894, 18 : 1153. 



v^agner's method i^or phosphoric acid 



201 



5 
I 1 



I. 



below. After filling to the mark with water it is shaken for half 
an hour and filtered. To 50 cubic centimeters of the filtrate are 
added 100 cubic centimeters of molybdic solution and the whole 
heated to 80°. After cooling, the precipitate is filtered and the 
phosphoric acid estimated in the usual way. 

The acid ammonium citrate solution used is made as follows: 
Dissolve 160 grams of citric acid with enough ammonia to repre- 
sent about 28 grams of nitrogen and make up with water to one 
liter. 

The molybdic solution is made by dissolving 125 grams of 
molybdic acid in a slight excess of 2.5 per cent, of ammonia, 
adding 400 grams of ammonium nitrate, diluting to one liter and 
pouring the solution into one liter of nitric acid having a specific 
gravity of 1.19. After allowing to stand at room temperature 
for one day the mixture is filtered and is then ready for use. 

175. Wagner's Method for Phosphoric Acid. — The directions giv- 
en by Wagner for determining the phosphoric acid in slags and 
raw phosphates soluble in citrate solutions are the following :^^ 
Five grams of the material as it is sent into commerce, without 
grinding or sifting, are placed in a half-liter flask, covered with 
nearly a quarter liter of water, and then 200 cubic centimeters of 
citrate solution added, prepared as described below. The flask 
is filled to the mark with water. The flasks, wdiich are of the 
shape shown in the figure, are closed wath rubber stoppers, and 
without delay placed for half an hour in a rotating apparatus, 
(Fig. II), which is turned on its axis from 30 to 40 times a min- 
ute. If a shaking apparatus be used instead of the one men- 
tioned, 200 cubic centimeters of the citrate solution should be 
placed in a half-liter flask, filled to the mark with water, and the 
contents poured into a liter flask containing the phosphate. This 
flask should be placed in a nearly horizontal position in the ap- 
paratus and the agitation be continued for half an hour. On 
removal from the apparatus the mixture is filtered and 50 cubic 
centimeters thereof treated with double that quantity of molybdic 
solution at 80° and the precipitate separated after cooling. The 
precipitate is carefully washed with one per cent, nitric acid mix- 

" Chemiker-Zeitung, 1894, 18 : 1933. 



I 



I: 



1 1 



\l 



•02 



AGRICULTURAL ANALYSIS 



tiire, after which the filter is broken and the precipitate washed 
into a beaker with two per cent, ammonia and the filter washed 
therewith until about lOO cubic centimeters have been used. If 
the solution is turbid from the presence of silicic acid it should be 
precipitated a second time by addition of molybdic solution. The 




Fig. n. Wagner's Digestion Apparatus for Slags. 

ammoniacal solution of the yellow precipitate is treated, drop by 
drop, with constant stirrinj2^, with 15 cubic centimeters of mag- 
nesia mixture, and set aside for two hours. The precipitate is 
collected, washed, ignited and weighed in the usual manner. The 
direct precipitation of the phosphoric acid by the magnesia solu- 
tion in presence of citrate is not advisable because of the almost 
general presence of silicic acid, which would cause the results to 
be too high. 

The chief objection to this method of Wagner lies in the fail- 
ure to control the tem])erature at which the digestion with citrate 
solution is made. Huston has shown, as will be described further 
on, that the temperature exercises a great influence in digestion 
with citrate. Since the laboratory temperature, especially in this 
country, may vary between 10° and 40°, it is evident that on the 
same sample the Wagner method would give very discordant re- 
sults at different seasons of the year unless the digestions were 
made at one temperature. In order to control the temperatures 



ANALYSIS OF BASIC SLAGS 



203 



of digestion, the apparatus devised by the author may be used.'^^ 
176. Solutions Employed in the Wagner Method.— i. Am- 
monium Citrate— h\ one liter there should be exactly 150 grams 
of citric acid and 27.93 grams of ammonia, equivalent to 23 
grams of nitrogen. The following example illustrates the prep- 
aration of 10 liters of the solution: In two liters of water and 
3.5 liters of eight per cent, ammonia, 1500 grams of citric acid 
are dissolved and the cooled solution made up exactly to eight 
liters. Dilute 25 cubic centimeters of this solution to 250 cubic 
centimeters and treat 25 cubic centimeters of this with three 
grams of calcined magnesia and distill into 40 cubic centimeters 
of half-normal sulfuric acid. Su])pose the ammonia nitrogen 
found corresponds to 20 cubic centimeters of fourth-normal soda- 

20.0X0.003 5 X 8000 
2.5 



lye. Then in the eight liters are contained 



=224 grams of ammonia nitrogen. In order to secure in 
the 10 liters the proper quantity of ammonia there must be added 
two liters of water containing 23a— 224=six grams of nitrogen 
or 7.3 grams ammonia ; viz., 94 cubic centimeters of 0.967 specific 

gravity. 

2. Molybdate Solution.— Dissolve 125 grams of molybdic acid 
in dilute 2.5 per cent, ammonia, avoiding a large excess of the 
solvent. Add 400 grams of ammonium nitrate, dilute with water to 
one liter and pour the solution into one liter of nitric acid of 1.19 
specific gravity. Allow the preparation to stand for 24 hours at 
35° and filter. 

3. Mai^ncsia Mixture. — Dissolve 1 10 grams of pure crystallized 
magnesium chlorid and 140 grams of ammonium chlorid in 700 
cubic centimeters of eight per cent, ammonia and 130 cubic centi- 
meters of w^ater. Allow to stand several days and filter. 

177. Analysis of Basic Slags by the Method of the German 
Agricultural Experiment Stations.— The methods of determining 
the fertilizing value of basic slags (Thomas Meal) have been 
studied by a committee of the German experiment stations.'^' 

^2 Principles and Practice of Agiicultural Analysis, 2nd P/lition, 1906, 

1 : 394- 

^* Warmer. Bestinimung der zitronensaureloslichen Phosphorsaure \n 

Thoniasmehlen, 1903. 



1 1 



\. s 



■! I 



^1 



204 



AGRICULTURAL ANALYSIS 



11 



li 



A full statement of the problem is ^iven in the first part of the 
report. Jn the second part the sources of error are discussed, 
together with the precautions to be observed in order that these 
errors may be avoided. In the third part are given the methods 
of procedure which in the opinion of the committee give the most 
acceptable results. 

These conclusions show : 

1. That the use of molybdic acid in separating the dissolved 
phosphate is generally unnecessary. 

2. The phosphate soluble in the citric acid employed should be 
precipitated immediately after its preparation. 

3. The precipitation should be accomplished by the iron-citrate- 
magnesia mixture to be described. 

4. The iron-citrate-magnesia mixture should be added with 
constant stirring. 

5. The shaker should have a speed of from 250 to 300 revolu- 
tions or vibrations a minute. 

6. The temperature of the mixture should not go above 18°. 

If the above rules are followed results are obtained which cor- 
respond with those secured by other exact methods. Even slags 
which have an exceptional content of silicic acid can be examined 
by this method with certainty in the results. It may be considered, 
therefore, that all the difficulties have been removed, and that a 
simple method of precipitation which, upon the whole, is much 
more reliable than those formerly employed, can be applied to the 
examination of basic phosphatic slags. The solutions employed 
are as follows : 

First. — Concentrated Citric Acid Solution, 10 Per Cent. Exact- 
ly one kilogram of chemically pure crystallized uneffloresced 
citric acid is dissolved in water, diluted to 10 liters, and for the 
purpose of preventing the growth of mould and other decom- 
position products, five grams of salicylic acid are dissolved in the 
mixture. 

Second.— Dilute Citric Acid Solution, Two Per Cent. Exactly 
one volume of the concentrated citric acid solution, above men- 
tioned, is diluted with four volumes of water. 

Third. — Molybdic Solution. One hundred and fifty grams of 



PREPARATION OF THE CITRIC ACID EXTRACT 



205 



11 



chemically pure ammonium molybdate are dissolved in about 500 
cubic centimeters of water. This solution is poured into one liter 
of nitric acid, 1.19 specific gravity, 400 grams of ammonium 
nitrate added thereto, and the mixture diluted with water to two 
liters. The solution is allowed to stand 24 hours at about 35° 
temperature and filtered. 

fourth.— Magnesia Mixture. One hundred and ten grams of 
crystallized magnesium chlorid and 140 of ammonium chlorid are 
dissolved in 1300 cubic centimeters of water and 700 cubic centi- 
meters of ammonia water containing eight per cent, of NH3 added 
thereto. After standing several days the solution is filtered. 

pifth.— Citrate-Magnesia Mixture. Two hundred grams of 
citric acid are dissolved in 20 per cent, of ammonia and the vol- 
ume made up to one liter with 20 per cent, ammonia. This solu- 
tion is mixed with one liter of the magnesia mixture described 
under " fourth.'' 

Sixth.— Iron-Citrate-Magnesia Mixture. One liter of the 
citrate-magnesia mixture described under ''fifth'' is mixed with 10 
cubic centimeters of a 20 per cent, ferrous chlorid solution. 

Preparation of the Basic Slag for Analysis.— Tht basic slag 
which is intended for analysis is passed through a two 
millimeter mesh sieve in order to remove any large pieces 
which may be present. All loss of dust during this operation is 
to be carefully avoided and to this end the sieve is to be closed 
with a well fitting cover and nicely adjusted to the vessel receiv- 
ing the sifted material. Any residue remaining upon the sieve is 
weighed and is excluded from analysis, but is included in the 
results on the total sample in order to determine the percentage 
thereof. Thus prepared the material will yield a typical sample 

for analysis. 

178. Preparation of the Citric Acid Extract.— Five grams of 
the basic slag, prepared as above, are placed in a half-liter flask 
into which previously five cubic centimeters of alcohol has been 
poured and the flask filled with the dilute two per cent, citric acid 
solution at a temperature of 17.5° the flask closed with a rubber 
stopper and without delay placed in a revolving shaking apparatus 
rotating at from 30 to 40 times a minute for 30 minutes. The con- 
tents of the flask are then immediately filtered. 



1- i 



I 
1 



M 

I. 

r 

t 

r 



2o6 



AGRICULTURAL ANALYSIS 



PREPARATION 01^ THK CITRIC ACID EXTRACT 



207 



179. Treatment of the Citric Acid Extract. — The filtrate ob- 
tained as above is^as soon as possible subjected to the following 
treatment : Fifty cnl)ic centimeters of the filtrate in a beaker are 
placed in a stutzer shakini^- apparatus, which is set in rapid mo- 
tion from about 250 to 300 vibrations per minute; 50 cubic centi- 
meters of the iron-citrate-ma^^^nesia mixture, al)ove noted, are 
tlien added, and with the tem])erature at from 14° to 18° 
the shaking is continued for half an hour. The precipitate is put 
in a gooch crucible or upon an ash-free filter, washed with two 
l)er cent, ammonia, ignited and weighed in the usual way. If 
the citric acid solution obtained above is exceptionally light col- 
ored or entirely colorless the duplicate estimation is not made 
according to the described method, but by the molybdate method 
or by the Naumann method. '^^ 

The molybdate method is carried out as follows : Fifty cubic cen- 
timeters in a beaker or flask are treated with from 50 to 80 cubic 
centimeters of the molybdic solution, above mentioned, and 
warmed in a water bath to about 65°. The beaker is then 
withdrawn from the water bath, cooled and its contents filtered, 
and the molybdic i)reci])itate carefully washed with a one per 
cent, nitric acid solution and dissolved in about 100 cubic centi- 
meters of two ])er cent, ammonia. The ammoniacal solution, with 
constant stirring, is treated with 15 cubic centimeters of the mag- 
nesia mixture, the beaker covered with a glass plate and set aside 
for two hours. The ])recipitated ammonium magnesia phosphate 
is collected u])on an ash-free filter or gooch, ashed with two 
per cent, ammonia, dried, the filter pa])er, if used, ashed over a 
bunsen burner and finally ignited in a blast for two minutes, 
cooled and weighed. 

180. Preparation of the Citric Acid Extract of Basic Slag. 
— The details of the prei)aration and treatment of the extract are 
im])ortant. It is self-evident that the citric acid solution with 
which the slag is treated must be prej^ared exactly as described, 
and thus must contain 20 grams of chemically ])ure crystallized 
uneftloresced citric acid to the liter. For the purpose of diminish- 
ing the amount of work it is advisable to keep on hand a quantity 

*»* Chemiker-Zeitung, 1903, 27 : 12, 27, 120, 155. ; 



of 10 per cent, citric acid solution, which is preserved by the ad- 
dition of half a gram of salicylic acid per liter. From this store 
the other solution of citric acid can be prepared. It is important 
that the citric acid solution which is used, should be as nearly as 
possible at a mean temperature of 17.5°. Any departure from this 
temperature is apt to produce errors. For this reason, the shaking 
machine should be in a room approximately of the same tem- 
perature. It is advisable to have the apparatus protected with 

felt. 

In pouring 500 cubic centimeters of citric acid solution on five 
grams of the sample it is sometimes noticed that small lumps 
of the slag are produced, which resist for a long while the en- 
trance of the solvent. For this reason it is advisable to use, pre- 
viously to the introduction of the citric acid solution, five cubic 
centimeters of alcohol into which the sample of basic slag is 

poured. 

It is inadvisable to use a shaking apparatus in place of the ro- 
tating apparatus described. Wagner uses a rotating apparatus 
made in Darmstadt, which is constructed of metal and driven by 
a gas motor. The flasks which are to be used in the rotating ap- 
paratus are made especially for this purpose according to the 
specifications of Wagner, and have a neck diameter of at least 
20 millimeters and the mark is at least eight centimeters 
below the mouth. Some care must be exercised in this matter, 
for if the diameter of the neck is too narrow or the mark too high, 
the movement of the fluid during rotation is restricted, and there- 
bv the results may be influenced. The rotating apparatus should 
have a velocity of from 30 to 40 rotations per minute, but any 
variation of the rate of rotation between these two figures is 
without any marked influence upon the results. 

The filtration ought to take place immediately after the end of 
the 30 minutes rotation, and it is advisable to use a folded filter 
of sufficient size so that the whole contents of the flask may be 
brought at once upon the filter. Small and badly working filters 
by reason of delay in the filtrations, can easily produce errors in the 
result. If the filtrate should be at first turbid, it is thrown back 
upon the filter. 



; ^1 



1 



208 



AGRICULTUEtAL ANALYSIS 



I 



II 



i8i. Remarks on the Conduct of the Direct Precipitation 
Method. — The citric acid extract of the basic slag changes by 
long standing, so far as the external appearance is concerned, 
very little. It remains for days either completely clear or only 
slightly turbid, without the production of any precipitate. In 
spite of this, however, important changes go on in relation to the 
application of the direct precipitation method, which consist in 
the fact that any silicic acid in the extract passes over into a pre- 
cipitable condition upon the addition of ammonia or ammoniacal 
citrate solution. The precipitability of the silicic acid increases 
from hour to hour, and it is therefore necessary to precipitate the 
filtrate extract immediately, or at longest, within an hour. 

The precipitability of silicic acid is greatly increased by heat. 
The shaking apparatus is, therefore, to be supplied with a water 
bath by which the mixtures during the summer time may be 
cooled. 

The precipitability of silicic acid is very little immediately after 
the citric acid solution of the phosphoric acid is made. The more, 
therefore, the precipitation of the phosphoric acid with the mag- 
nesia mixture is hastened, the more certainlv is avoided anv con- 
tamination of the precipitate with silicic acid. The precipitation 
of the phosphoric acid is also hastened as follows : 

a. If the ammoniacal citrate solution is not added first, and 
then the magnesia mixture, but the mixture of both is added to 
the citric acid extract ; 

b. The iron-citrate-magnesia mixture is poured into the citric 
acid extract in the shaking apparatus, which is already in active 
movement ; 

c. The shaking apparatus is to be placed in the shortest pos- 
sible time at its maximum vibration of from 250 to 300 vibra- 
tions per minute. 

The precipitability of the silicic acid is heightened through a 
lack of iron in solutions which are rich in silicic acid and poor in 
iron, therefore a pure precipitate is obtained only when the iron- 
citrate-magnesia mixture is employed. 

182. The Conduct of the Molybdate Method.— a. Great care must 



GERMAN METHOD FOR SLAGS RICH IN SILICIC ACID 209 



be exercised that the reagents employed in the preparation of the 
molybdic solutions be absolutely pure. 

b. Molybdic solutions before using should be tested for purity 
by means of a solution of disodium phosphate. 

c. The mixture of the citric acid extract and the molybdic solu- 
tion is to be taken from the water bath when the prescribed 
temperature has been reached. If the time of digestion be mark- 
edly extended a contamination of the precipitate with silicic acid 
arises, especially when the citric acid extract is not in a fresh 
condition, but only after from six to 12 hours standing is 
treated with the molybdic solution. 

d. A contamination of the molybdic precipitate with the silicic 
acid is recognized by the following: Slow solution of the pre- 
cipitate in ammonia and the production of a solution not com- 
pletely clear or becoming only slowly so. Under these condi- 
tions the process already advised, namely, a reprecipitation of 

the magnesia precipitate, is to be applied. 

183. The Official German Method for Slags Rich in Silicic Acid. 
— When the slags are very rich in soluble silicic acid the process 
of analysis is conducted as follows '^^ 

The sample is to be tested for silicic acid by the method of Kell- 
iier, which consists in boiling for one minute 50 cubic centime- 
ters of the citric acid extract with 50 cubic centimeters of ammo- 
niacal citrate solution and allowing to stand for a few minutes.^® 
If there is sufficient silicic acid present to interfere with the direct 
(Bottcher) precipitation of the phosphoric acid, a precipitate 
is separated which is not entirely soluble in hydrochloric acid. 
The ammoniacal citrate solution, employed above, contains in 10 
liters, 1 100 grams of nitric acid, 4000 grams of 24 per cent, am- 
monia, and water to the mark. 

The presence of a disturbing amount of silicic acid having 
been thus determined, it is separated in the following manner: 
To 100 cubic centimeters of the citric acid extract of the slag 
pre added 7.5 cubic centimeters of hydrochloric acid of 1.12 
specific gravity or five cubic centimeters of fuming h\(lrochloric 

^^ Die landwirtschaftUclien Versuchs-Stationeii, 1904, 60 : 374; 1905, 
61 :35i. 

^^ Chemiker-Zeitung, 1902, 26 : 1151. 



if 



■Si 



S 2 



> I 



t ,; 



i 



2IO 



AGRICULTURAI^ ANALYSIS 



SKPARATION OF SILICIC ACID 



211 



acid and the mixture evaporated to a thick sirup, smelHng of hy- 
drochloric acid. To the hot residue, from 1.5 to two cubic centi- 
meters of hydrochloric acid, 1.12 specific gravity, are added, and 
the mixture thoroughly stirred and dissolved in enough water to 
make the volume 100 cubic centimeters. The i)hosphoric acid is 
determined in 50 cubic centimeters of the filtrate by the direct 

method. 

The process consists in adding 50 cubic centimeters of the 
citrate-magnesia mixture to the same volume of the filtered citric 
acid extract of the slag. The magnesia mixture contains 550 
grams of magnesium chlorid and 700 grams of ammonium chlorid 
dissolved in 3.5 liters of eight per cent, ammonia, and 6.5 liters 
of water. The ammoniacal citrate solution for mixing with the 
magnesia mixture, mentioned above, contains 2000 grams of citric 
acid dissolved in 20 per cent, ammonia, and the volume made up 
to 10 liters with the same reagent. Before use, equal parts of 
the magnesia mixture and the ammoniacal citrate solution are 
mixed together. 

184. Bottcher Method. — The Bottcher modification of the direct 
citrate method of determining the phosphoric acid dissolved from 
basic slags by citric acid is as follows :"'" 

In 50 cubic centimeters of the solution of a slag in citric acid 
according to Wagner's method, the phosphoric acid is thrown 
down in the prescribed manner by magnesium citrate solution, 
the i)recipitate collected on a filter, washed several times with 
five ])cr cent, ammonia, and the moist filter ashed. The ash is 
dissolved in warm hydrochloric acid, the dilute solution passed 
through a small filter, washed with hot water, and the phosphoric 
acid again precipitated with the citrate magnesia. 

The important ])oint is that after the addition of the citrate of 
magnesia, the mixture be immediately vigorously shaken and then, 
without a moment's delay, filtered. Even standing for from 
half an hour to an hour may cause serious annoyance and intro- 
duce serious errors into the results. 

The direct precipitation of the phosphoric acid by ammoniacal 
citrate of magnesia was adopted as the official method in the 
" Chemiker-Zeitung, 1897, 21 1: 168. 



general meeting of the delegates of the German agricultural ex- 
periment stations, at Cassel, in 1903, both for slags and tricalcium 
phosphates, and for the general separation of phosphoric acid.^^ 

Bottcher, in a later communication, expresses the opinion that 
if the direct precipitation of the phos])horic acid be carried on 
with all the promptitude which he has recommended, the pre- 
vious separation of the silicic acid, when an excess has been in- 
dicated by the Keliner test, is rarely necessary. •'^^" 

The great point to be observed is that all the manipulations be 
conducted without delay. The preliminary test by the Keliner 
method is chiefiy valuable in showing with whai samples special 
precautions are necessary. 

185. Separation of Silicic Acid in the Estimation of Phosphoric 
Acid in Basic Slag, Bone Meal, Etc."*^ — Attention is called by 
Bottcher to the fact that after the Association of Agricultural 
Experiment Stations of the German Empire had determined to 
estimate the citric-acid-soiuble phosphoric acid in basic slag by 
the direct precipitation method in all cases where the preliminary 
test by boiling with 50 cubic centimeters of ammoniacal citrate 
solution did not show a high content of silicic acid, the opinion 
has again come into consideration that the separation of the silicic 
acid by evaporation with hydrochloric acid is necessary wdth all 
basic slags because the direct precipitation sometimes gives re- 
sults which are too high, even if the preliminary test shows no 
'especially high content of silicic acid, and the solutions very often 
filter too slowlv. l>6ttcher, however, affirms anew that the 
conduct of the direct precipitation citrate method never leads to 
any difficulties of filtration nor to any differences in the results. 
As he pointed out in a former place, and as he has shown by 
subsequent analyses, which are given, he has obtained absolutely 
correct results with all normal basic slags, which with two per cent, 
citric acid solution gave bright green solutions, even when the pre- 
liminary treatment has shown a high content of silica."^ In 

^"^ Die landwirtschaftlichen Versuchs-Stationen, 1904, 60 : 221. 
^^ Chemiker-Zeitung, 1903, 27 : 247. 

Zeitschrift fiir an^^ewandte Chemie, 1904. 17 1988. 
•^ Chetniker- Zeitung, 1905, 29 : 1293. 
*" Chemiker-Zeitung, 1903, 27 : 247. 






I 



» ? 



A\ 



212 



AGRICULTURAL ANALYSIS 



all cases, however, the method which he has proposed must be 
carefully followed out, that is, all the manipulations must follow 
each other directly without delay, a condition which is easily se- 
cured. If, on the contrary, the citric acid extract, or the pre- 
cipitations with citrate solution and magnesia mixture, or the 
citrate-holding magnesia mixture, are allowed to stand for several 
hours, which, in spite of the precise directions given, still some- 
times happens, it can readily occur that large quantities of silicic 
acid come down with the phosphoric acid precipitate and the re- 
sults are, in consequence, too high. In such cases it is easy to ex- 
plain why the precipitated phosphoric acids filter badly. In 
carrying out of the method in cases of bad filtration, it has been 
observed by Bottcher, in the conduct of over 800 determinations, 
that if a solution filters badly it is a proof that in some way or 
other silicic acid has been precipitated, and naturally in such a 
case, the silicic acid must be removed by evaporation with hydro- 
chloric acid in order that correct results be obtained. 

Many comparisons are given by the author of the data obtained 
by direct precipitation and by precipitation after the separation 
of the silicic acid. The dififerences are in all cases negligible 
between the two methods. 

Following are the data from two samples in which the magnesia 
pyrophosphate was obtained by four diflferent methods, namely: 

(1) Direct precipitation. 

(2) Direct precipitation after separation of silicic acid. 

(3) Direct precipitation by molybdate method. 

• (4) Direct precipitation by molybdate method after separation 
with silicic acid. 

The data obtained are as follows : 



Weight of Sample I. 


Weight of Sample II 


Grams. 


Grams. 


Method (l) 0.1472 


0.1435 


(2) 0.1466 


0. 1410 


(3) 0.1475 


0.1420 


(4) 0.1476 


0.1436 



These analytical data show that basic slags which are not 
capable of being correctly analyzed by the direct citrate precipita- 
tion method are of very seldom occurrence. Nevertheless a pre- 



DIRECT AND MOLYBDATE METHODS 



213 



liminary treatment by the citric acid test for silicic acid should 
not be omitted, since it is a safe means of discovering those 
samples which must be treated with particular care. 

186. Comparison of the Direct and the Molybdate Method for the 
Estimation of the Total Phosphoric Acid in Basic Slag, Bone 
Meal, Etc.'"-— V. Schenke has stated that the direct precipitation 
of total phosphoric acid in bone meal and basic slags, according 
to the method of the Association of Agricultural Experiment 
Stations of Germany, that is, direct precipitation of magnesia 
mixture, gives from 0.3 to 0.4 per cent, less phosphoric acid than 
the molybdate method.«^ He, therefore, considers it necessary that 
the strongly acid phosphate solution before precipitation with 
magnesia mixture should be almost neutralized and only half the 
quantity, namely, 50 cubic centimeters instead of 100 cubic centi- 
meters, should be treated with the ammonium citrate solution. 
It has, however, already been shown by the earlier data of 
Maercker and Halenke, as well as by the latest researches of 
Mach®* that this view of Schenke is not correct, and also the 
analvses of Bottcher indicate the same fact, and that neutraliza- 
tion of the solution before the precipitation with the citrate solu- 
tion and the magnesia mixture either by aqua regia or by sulfuric 
acid is not necessary.^^ Bottcher says it is claimed by many ana- 
lysts that by solution of bone meal, etc., with aqua regia and subse- 
quent direct precipitation with citrate solution and magnesia mix- 
ture, incorrect and, indeed, higher results are obtained than 
when sulfuric acid is used for the solution. As a reason for 
this it is said that the compensation for the errors which take 
place in the aqua regia solutions is irregular, according to the kind 
and quantity of the bases which are present in the solution. It 
is also supposed that in bone meals and other organic substances 
by reason of the incomplete oxidation with aqua regia, organic 
acids are formed whose lime salts are equally soluble in the am- 
monium citrate solution and are, therefore, carried down by the 
precipitate. In the solutions by sulfuric acid the proportions re- 

«'^ Cheiniker-Zeitun^'. 1905, 29 : 1294. 

^ Die landvvirtschaftlichen Versuchs-Stationen, T905, 62 : 3. 
«♦ Die landwirtschaftlirhen Versuchs-Stationen, 1905-6, 63 : 81. 
^ Cheiiiiker-Zeitung, 1905, 29 : 1294. 



i 1 



■ n 



i\ 






! M 



214 



AGRICULTURAL ANALYSIS 



TOTAL PHOSPHORIC ACID IN BASIC SLAGS 



215 



main essentially more favorable, since not all, but always an equal- 
ly proportionate part, of the bases ^o into solution. 

In order to prove whether these objections against the solution 
with acpia regia were correct, Uottcher in different bone meals 
carried out the estimation of the total phosphoric acid, both by 
solution with arpia reg-ia and with sulfuric acid. In samples of 
50 cubic centimeters of the acid phosphate solution the phosphoric 
acid was i)recipitated, according to the methods of the German 
association, by direct precipitation with citrate solution and 
magnesia mixture, and in other samples of 50 cubic centimeters 
according to the modification of Schenke, that is, the approximate 
neutralization of the solutions with ammonia ])efore the addition 
of the citrate solution and magnesia mixture. 

The data which were obtained show that the objections urged 
by Schenke are not well founded and that in the case of bone 
meals, etc., as good results were obtained by solution with aqua 
regia as with sulfuric acid. If sometimes lower results are ob- 
tained after solution in sulfuric acid, the reason lies perhaps in 
the fact that after the treatment of strong sulfuric acid phosphate 
solutions with ammoniacal citrate solution a marked heating of the 
mixture takes place and it is not sufficiently cooled before the 
addition of the magnesia mixture. This subsequent cooling be- 
fore precipitation is necessary since otherwise the results fall 
too low. 

187. Estimation of Phosphoric Acid in Slags.— The further 
discussion of determining the phosphoric acid in slags by the cit- 
rate method by Schenke and Mach has introduced certain modi- 
fications of an unimportant character, in the process."" 

In the estimation of the citrate-soluble phosphoric acid in slags 
by the molybdate method, Schenke follows in general the Wagner 
method, heating the precipitate only 15 to 30 minutes in a water 
l)ath at 80^ or 90° and allowing to cool for two or three hours. 
Wy this method the precipitation of molybdic acid is most cer- 
tainly avoided and a bright and clear solution of the precipitate 
is easily secured in cold dilute ammonia. Impurities due to 
silicic acid are also avoided. 

^4 y^ie landwirtschaftlichcn Versudis-Stationen, 1905, 62 : 3 ; 1906. 



In all cases the complete precipitation of phosphoric acid is 
rendered certain by an addition of moly])date solution to the fil- 
trate. 

Schenke calls attention to the important point that if the method 
of the German stations is strictly followed with the citrate method 
of determination no precipitate at all of phosphoric acid is ob- 
tained where only very small cjuantities are present. This is the 
case both with certain soils which contain only a trace of phos- 
phoric acid and certain cattle foods. In such cases the above 
stated molybdate method gave agreeing results even in these small 
c[uantities. The reason for this is said to be the increased solu- 
bility of the precipitate of magnesium ammonium phosphate in 
the double quantity of ammonium citrate solution which is used. 

188. Estimation of Total Phosphoric Acid in Basic Slags Solu- 
ble in Citric Acid Solutions.— Since the value of basic slag is no 
longer determined solely by the total content of phosphoric acid . 
therein, the agricultural analysts have never been able to agree 
upon a satisfactory plan for the valuation of phosphoric acid 
available for plant growth. The use of citric acid solutions for 
dissolving the supposed available phosphoric acid is the one which 
is most commonly employed. It is easily seen, however, that 
the activitv of a solution of this kind depends upon the amount of 
free lime in the sample, its state of subdivision, the temperature 
rt which the solution takes place and the agitation to which the 
mixture is subjected. The disturbing influence of silicic acid is 
also to be taken into consideration and this has been fully dis- 
cussed. Mach has found in a large number of determinations 
that the Wagner method in most cases gives satisfactory results 
while the direct precipitation by the Bottcher method sometimes 
fails, and in its present form is not to be regarded as reliable as 
the German experiment station method with previous separa- 
tion of silica.''' It is concluded, therefore, that as a result of the 
study of all the various methods, the one which is based upon the 
])revious separation of the silicic out of the citric acid extract is 

the most reliable. 

In a study of the different forms of precipitation of total phos- 

*' Die landwirtschaftlichen Versuchs-Stationen, 1905-6, 63 : 81. 



:| 



2l6 



AGRICULTURAL ANALYSIS 



GERMAN manufacturers' METHOD 



217 



plioric acid in basic slags, Mach also found that while some forms 
of the citric incLliud of direct precipitation gave very good results, 
the molybdate method, especially in the case of sulfuric acid solu- 
tions of slags, must be regarded, without doubt, as the most re- 
hable. 

189. Association and Other American Methods for Basic Slag. 
— The question of adopting a method for determining the avail- 
ability of phosphoric acid in slag, has been before the Association 
of Official Agricultural Chemists for the past three years, and 
quite a number of reagents and processes have been proposed for 
this purpose. The practical absence of this form of fertilizer 
from the American market has prevented the manifestation of 
much interest in the discussion. vSolubility has been determined 
in 1.09 ammonium citrate, in one per cent, citric acid, in two per 
cent, citric acid, and in all these after preliminary treatment with 
water or with five per cent, sugar solution followed by five per 
cent, ammonuim chlorid solution as suggested by Macfarlane.®* 
The referee for 1902 shows that the Wagner method indicates 
about 80 per cent, of the phosphoric acid in slag as available and 
the ammonium citrate method, 30 per cent. The former is regarded 
as too high, and the latter, too low. He suggests that a percentage 
be established that may be regarded as representing the amount 
of availability, and a method could then be devised to give this 
amount. '^^ While no action was taken, the sentiment of the asso- 
ciation appeared to be in favor of a valuation based on the deter- 
mination of phosphoric acid and of fineness as is now the usage 
in the case of raw bone. 

Hilgard has called attention to the increasing use of phosphatic 
slags in California and attributes their good efl^ects to the large 
quantity of lime in the arid soils. This condition secures the 
reversion of the water-soluble acid in superphosphates within 
the first three or four inches of the surface of the soil. Deep 
plowing is, therefore, necessary to bring the phosphoric acid into 
contact with the lower roots of the crop. Such plowing would 
also mix basic phosphates with the deeper layers of the soil, and 

^ Division of Chemistry, Bulletin 62, 1901 : 46. 
«' Bureau of Chemistry, Bulletin 73, 1903 : 16. 



since the slags are cheaper than the superphosphates in California, 
he recommends their use. He is also in accord with the senti- 
ment of the association to value these basic slags, at least provi- 
sionally, by their total content in phosphoric acid and their degree 
of fineness.''*^ 

Huston and Jones show that the strength of citric acid, time 
and temperature of digestion, all exert a marked effect on the 
amount of phosphoric acid dissolved from slags, as does also the 
lelation of quantity of material to volume of solvent. ^^ It was 
found that even when basicity of the slag was corrected the 
reaction with citric acid was far from complete in 30 minutes at 
a temperature of 65°. The same conclusion holds with neutral 
ammonium citrate, though here the differences are not so marked. 
The work indicates that in a relatively short time all the phos- 
phoric acid will be dissolved, even by dilute citric acid at any 
temperature, this indicating, further, that the phosphate of basic 
slag has practically a uniform composition. 

190. German Manufacturers' Method. — In the examination 
of phosphatic slags, the Union of German Fertilizer Manufac- 
turers determine total phosphatic acid after solution, (a) in 
hydrochloric acid, and (b) in sulfuric acid. In the hydrochloric 
acid method 10 grams of finely ground phosphatic slag, which has 
passed through a two millimeter sieve, are placed in a flask of 
one-half liter capacity, 80 cubic centimeters of concentrated hy- 
drochloric acid added and the mixture evaporated on a sand-bath 
to a sirupy consistence. The mixture is dissolved in water, treated 
with a few drops of hydrochloric acid, and after cooling the flask 
is filled to the mark. In 50 cubic centimeters of the filtrate, after 
the addition of 100 cubic centimeters of the ammonia-citric acid 
solution, made up according to the method of Maercker, namely, 
1500 grams of citric acid, 5000 cubic centimeters of 24 per cent, 
ammonia and water to 15 liters, the phosphoric acid is now pre- 
cipitated by 25 cubic centimeters of the ordinary magnesia mix- 
ture, stirred for one-half hour in a shaking a|)paratus, and after 
standing two hours, filtered and treated as has already been de- 
scribed for the estimation of phosphoric acid soluble in water. 

''^ Bureau of Chemistry, Bulletin 81, 1904 : 169. 
" Division of Chemistry, Bulletin 49, 1897 : 68. 



J I 



Mi 



2l8 



AGRICULTURAL ANALYSIS 



I 



>w 



It 



I 



In the sulfuric acid method, lo grams of phosphatic slag, pre- 
pared as ahove descrihed, are covered with a few cubic centi- 
meters of sulfuric acid (one to two) and well shaken. After the 
addition of 50 cubic centimeters of concentrated sulfuric acid, the 
mixture is heated at first to boiling and afterwards just to the 
boiling point, until the mass is eva])orated to a thick fluid and vio- 
lent l)umj)ing begins. After cooling, water is gradually added to 
the mark and the phosphoric acid determined either by the citrate 
or molybdic acid method. 

Estiiiiaiioii of Citric-Acid-Sohiblc Phosphoric Acid in Basic 
Slag. — The method of estimating the citric acid soluble i)hos- 
phoric acid in basic slag is that of Wagner, which has already 
been described. 

191. Estimation of Lime. — When the lime is to be determined 
in basic slags, some dithculty may be experienced by reason of 
danger of contamination of the oxalate precipitate with iron and 
especially manganese, which is often present in slags. 

Holleman ])r()poses to estimate the lime in ])asic slag by mod- 
ilication of the methods of Classen and Jones.'- The manipula- 
tion is as follows: Fifty cubic centimeters of an acid solution 
of slag, from which the separated silica has been removed by fil- 
tration, equivalent to one gram of substance, are evaporated to a 
small volume, 20 cubic centimeters of neutral ammonium oxalate 
solution (one to three) added to the residue and heated on a 
water bath, with frecpient stirring, until the ])recipitate is pure 
white and free from lum]")s. 'Hie time recjuired is usually about, 
10 minutes. The i)recipitate is collected on a filter and washed 
with liot water until the filtrate contains no oxalic acid. The 
precipitated calcium oxalate must be snow-white. The filter is 
broken and the calcium oxalate washed through, first with water 
and finally with warm, dilute hydrochloric acid (one to one), 
The calcium oxalate is dissolved by adding 15 cubic centimeters 
of concentrated hydrochloric acid, the solution evaporated to a 
volume of about 25 cubic centimeters, and 10 cubic centimeters 
of dilute sulfuric acid (one to five), and 150 cubic centimeters 
of 96 per cent, alcohol added. After standing three hours or 
" Chemiker-Zeitung, 1892, 16 : 1471. 



ADULTERATION OF PHOSPHATIC SLAGS 



219 



more the precipitate is separated by filtration and washed with 96 
per cent, alcohol until the washings show no acid reaction with 
methyl orange. The calcium sulfate precipitated is dried to con- 
stant weight. This method gives a pure precipitate of calcium 
sulfate, containing only traces of manganese. 

192. Estimation of Caustic Lime. — The lime mechanically 
present in basic slags is likely to be found as oxid or hydroxid, 
especiallv when the sample is of recent manufacture. In the form 
of oxid the lime may be determined by solution in sugar. In this 
process one gram of the fine slag meal is shaken for some time 
with a solution of sugar, as suggested by Stone and Scheuch.'^ 
The dissolved lime may be titrated directly with standard hydro- 
chloric acid, or the lime is separated as oxalate from the hydro- 
chloric acid solution by treatment of the solution with ammonium 
oxalate. The calcium oxalate may be determined by ignition in 
the usual way or volumetrically by solution in sulfuric acid and 
titration of the free oxalic acid with potassium permanganate 
solutions. The standard solution of ])ermanganate should be of 
such a strength as to have one cubic centimeter equivalent to 
about 0.01 gram of iron. The iron value of the permanj^^anate 
used multiplied by 0.5 will give the quantity of calcium oxid 
fcnmd. 

193. Detection of Adulteration of Phosphatic Slags. — The high 
agricultural value of phosphatic slags has led to their adultera- 
tion and even to the substitution of other bodies. Several patents 
have also been granted for the manufacture of artificial slags of 
a value said to be an approximation to that of the by-products 
01 the basic pig iron process. 

(i) Method of Blum. — One of the earliest methods of exam- 
ining basic slag for adulterations is the method of Rlum.'* This 
method rests upon the principle of the determination of the car- 
bon dioxid in the sample. The basic phosphatic slag is supposed 
to contain no carbon dioxid. This is true only in case it is 
freshly prepared. The tetrabasic phos])liate, after being kept 
for some time, gradually al)sorbs carbon dioxid from the air. As 
high as 19 per cent, of carbon dioxid have been found in slags 

" Journal of the American Chemical Society, 1894, 16 : 721. 
'* Zeitschrift fiir analytische Chemie, 1890, 29 : 408. 






220 



AGRICULTURAL ANALYSIS 



which have been kept for a long while. When the slag has ab- 
sorbed so much of carbon dioxid and water from the air as to 
be no longer profitable for market, it can be restored to its orig- 
inal condition by ignition. Any great loss on ignition is a ground 
for suspicion concerning the purity and utility of a slag. 

(2) Method of Richtcrs-Forster. — One of the common adulter- 
ants of tetrabasic phosphate is aluminum (Rodonda) phosphate. 
The method of detecting this when mixed with the slag is de- 
scribed by Richters-Forster."^^ The method depends on the fact 
that soda-lye dissolves the aluminum phosphate, although it does 
not dissolve any calcium phosphoric acid from the slag. Two 
grams of the sam])le to be tested are treated with 10 cubic centi- 
meters of soda-lye of from 7° to 8° B. in a small vessel, with 
frequent shaking, for a few hours at room temperature. After 
filtration the filtrate is made acid with hydrochloric and afterwards, 
slightly alkaline with ammonia. With pure basic slag there is a 
small trace of precipitate produced, but this is due to a little silica, 
which can be dissolved in a slight excess of acetic acid. If, 
however, the basic slag contains aluminum phosphate, a dense 
jelly-like precipitate of aluminum phosphate is produced. 

(3) Method of Jensch. — Edmund Jensch determines the tera- 
basic phosphate in slags by solution in organic acids, and pre- 
fers citric acid for this purpose.'^ This method was also recom- 
mended by P)lum.'^ 

It is well known that the tetrabasic phosphate in slags is com- 
pletely soluble in citric acid, while the tribasic phosphate is only 
slightly, if at all, attacked. The neutral ammonium salts^of or- 
ganic acids do not at first attack the tribasic phosphate at all, 
and they do not completely dissolve the tetrabasic phosphate. 
The solution used by Jensch is made as follows : Fifty grams of 
crystallized citric acid are dissolved in one liter of water. A 
weaker acid dissolves the tetrabasic phosphate too slowly and a 
stronger one attacks the tribasic phosphate present. 

■'^ Mitteilungen der deutschen Landwirtschafts-Gesellschaft, 1890-91, 
6 : 131. 

Zeitschrift fiir augewandte Chemie, 1890, 3 : 595. 
'* Zeitschrift fiir an^ewandte Chemie, 1889, 2 : 299. 
" Zeitschrift fiir analytische Chemie, 1890, 29 : 409. 



ADULTERATION OF PHOSPHATIC SLAGS 



221 



78 



Schucht recommends the following method of procedure.' 
One gram of the slag, finely ground, is treated in a beaker glass 
with about 150 cubic centimeters of Jensch's citric acid solution 
and warmed for 12 hours in an air-batii at from 50° to 70° 
with frequent shaking. Afterwards it is diluted with 100 cubic 
centimeters of water, boiled for one minute and filtered. The 
filter is washed thoroughly with hot water and the phosphoric 
acid is estimated in the filtrate in the usual way. W^ith artificial 
mixtures of basic slags and other phosphates, the quantity of basic 
slag can be determined by the above method. 

(4) Method of IVrampelmeyer.— According to WVampelmeyer, 
the most convenient method for discovering the adulteration of 
basic slag is the use of the microscope.'" All finely ground nat- 
ural phosphates are light colored and with a strong magnifica- 
tion, appear as rounded masses. In basic slags the particles are 
mostly black, but there are often found red-colored fragments 
having sharp angles, which retract the light in a peculiar way, 
so that, with a very little experience, they can be recognized as 
being distinctive marks of pure basic slag. 

In artificial mixtures of these two phosphates, which we have 
made in the laboratory of the Division of Chemistry, we have been 
able to detect with certainty as little as one per cent, of added 
mineral phosphate. 

One form of adulterating natural mineral phosphates has been 
mixing them with finely pulverized charcoal or soot to give them 
the black appearance characteristic of the basic slags. This 
form of adulteration is at once disclosed by simple ignition or by 
microscopic examination. 

(5) Loss on Ignition. — If all doubts cannot be removed by the 
use of the microscope, the loss on ignition should be estimated. 
Natural phosphates all give a high loss on ignition, ranging from 
eight to 24 per cent., while a basic slag gives only a very slight 
loss on ignition, especially when fresh. A basic slag which has 
stood for a long while and absorbed carbon dioxid and moisture, 
may give a loss on ignition approximating, in a maximum case, 
the minimum loss on ignition from a natural phosphate. 

'» Zeitschrift fiir an^ewandte Chemie, 1890, 3 : 594- 

'» Die landwirtschaftlicheii Versiichs-Slationen, 1894, 43 : 183. 



11 









222 



AGRICULTURAL ANALYSIS 



I 



III 



In experiments made m the laboratory of the Division of Chem- 
istry in testing for loss on ignition, we have uniformly found 
that natural mineral phosphates will lose from nearly one to 2.5 
times as much on ignition as a basic slag which has been kept 
for two years. A basic slag in the laboratory more than two 
years old gave, as loss on ignition, 4.12 per cent. Several sam- 
ples of finely ground I'lorida ])h()S])hates gave the following per- 
centages of loss on ignition, as compared with a sample of slag: 

Odorless phosphate (slag), 4.12. 

Florida phosphates, 8.06, 6.90, 9.58, 6.40, 10.38 and 10.67, re- 
spectively. 

There are some mineral phosphates, however, which are ig- 
nited before being sent to the market. We have had one such sam- 
ple in the laboratory from P'lorida which gave, on ignition, a loss 
of only 1.4 ])er cent. In this case it is seen that the application of 
the process of ignition would not discriminate between a basic 
slag and a mineral phosphate. 

It may often be of interest to know what part of the loss, on 
ignition, is due to loosely held water in form of moisture. In 
such cases the sample should first be dried to constant weight 
and then ignited. In the following data are found the results 
obtained with samples treated as above indicated and also ignited 
directly. Number one is a basic slag two years old and the others 
are Florida phosphates. 

Heated to ioo° C. then ignited. Ignited directly. 

Lo.«;sat I^oss on Total I.oss on 

100° C. ignition. los.s. ignition. 

No. I (Slas:) 2.57 1.77 4.^4 4.J2 

No. 2 (Rock) 2.61 5.19 7.80 8.06 

No. 3 " 1.09 5.77 6.86 6.90 

No. 4 *' 0.42 9.20 9.62 9.58 

No. 5 •• 1. 81 4.83 6.64 6.40 

No. 6 •• 4.36 6.52 10.88 10.83 

No. 7 " 331 7.01 10.32 10.67 

(6) Presence of Siilfids.— Another point noticed in the labora- 
tory of the Division of Chemistry is that the basic slags uniformly 
contain sulfids which are decomposed upon the addition of an 
acid with an evolution of hydrogen sulfid. 

(7) Presence of Phiorin.—\n a])plying the test for fluorin, it 
has been uniformly found here, that the mineral phosphates respond 



ADULTERATION 01^ PHOSPHATIC SLAGS 223 

to the fluorin test, while the basic slags, on the contrary, respond 
to the hydrogen sulfid test. This test, however, was applied only 
to the few samples we have had and may not be a uniform 

property. r 1 1 

The absence of fluorin might not prove the absence ot adul- 
teration, but its presence would, I believe, certainly prove the 
fact of the adulteration in that particular sam])le. 

The fluorin test is applied by Hottcher in the following man- 
ner :^^ From 10 to 15 grams of the slag are placed in a beaker 
10 centimeters high and from five to six centimeters in diam- 
eter, with 15 cubic centimeters of concentrated sulfuric acid, 
stirred with a glass rod, and covered with a watch-glass, on the 
under side of which a drop of water hangs. If there be formed 
upon the drop of water a white murky rim, it is proof that a 
mineral phosphate containing fluorin has been added. After from 
five to 10 minutes you can notice on the clean watch-glass the 
etching produced by the hydrofluoric acid. According to Bottcher 
an adulteration of 10 per cent, of raw phosphate in slag can be 
detected bv this method. 

(8) Solubility in [^afrr.— Solubility in water is also a good 
indication, natural phosphates being totally insoluble in water, 
while a considerable quantity of the basic slag will be dissolved 
in water on account of the calcium oxid or hydroxid which it 
contains. If the loss on ignition is low, and the volume-weight 
and water-solubility high, the analyst may be certain that the 

sample is a pure slag. 

In comparative tests made in the laboratory of the Division of 
Chemistry with a sample of basic slag and seven samples of 
Florida phosphate, the percentages of material dissolved by water 
and by a five per cent, solution of citric acid were found to be as 
follows : 

Water-soluble. Soluble in 5 Per cent, citric acid 

Per cent. Per cent. 

Basic slag 0.97 16.10 

Florida phosphate o.oi 4-15 

'« '* 0.09 406 

«« «« 0.02 3-43 

«« «« 0.08 3-6^ 

«• •« 0.02 3-79 

«« •« 0.05 446 

«« «* 0.02 4-24 

^^^ Chemiker-Zeitung, 1894, 18 : 565- 



n 
I 



524 



AGRICULTUR/\L ANALYSIS 



From the above data it is seen that the solvent action of water 
especially would be of value, inasmuch as it dissolves only a mere 
trace of the mineral phosphates, approximating one per cent, of 
the amount dissolved from basic slag. In the case of the citric 
acid it is found that the amount of materials soluble in this sol- 
vent for basic slag is fully four times as great as for the mineral 
phosphates. Both of these processes, therefore, have considera- 
ble value for discriminating between the pure and adulterated 
article of basic slag. 

(9) Specific Gravity. — The estimation of the specific gravity 
is also a good indication for judging of the purity of the slag. 
This is best done by weighing directly a given volume. Basic 
slag will have a specific gravity of about 1.9, while natural phos- 
phates will have about 1.6. 

(10) Conclusions. — From the above resume of the standard 
methods which are in use for determining the adulteration of 
basic slag, it is seen that there are many cases in which grave 
doubt might exist even after the careful application of all the 
methods mentioned. If we had only to consider the adulteration 
of basic slag with certain of the mineral phosphates, that is, tri- 
calcium phosphate, the problem would be an easy one, but when 
we add to this the fact that iron and aluminum phosphates are 
employed in the adulteration, and that artificial slags may be so 
used, the question becomes more involved. 

Of tlie single tests, examination with the microscope appears 
to be the most fruitful. 

In doubtful cases, one after another of the methods should be 
applied until there is no doubt whatever of the judgment which 
should be rendered. 

DETERMINATION OF OTHER CONSTITUENTS IN 

NATURAL PHOSPHATES 
194. Water and Org-anic Matters.— The sample used for deter- 
mining water and organic matters, according to the practice of 
Chatard, should be ground fine enough to leave no residue on 
an 80 mesh sieve, and should be thoroughly mixed by passing it 
three times through a 40 mesh sieve.®^ 

»» Transactions of the American Institute of Mining Engineers, 1892-93, 



^^ 



CARBON DIOXID 



225 



Two grams are placed in a tared platinum crucible, which, 
with its lid, is placed in an air bath at 105° and heated for at 
least three hours. The lid is then put on, and the crucible is 
placed in a desiccator and weighed as soon as cold. The loss m 
weight is the moisture. The organic matter is determined as 

below. • 1 u 

Wyatt recommends that two grams of the fine material be 
heated in ground watch-glasses, the edges of which are separated 
so as to allow the escape of the moisture.'^- The heating is con- 
tinued for three hours at 110°, the watch-glasses then closed 
and held by the clip, cooled in a desiccator, and weighed. This 
method is excellent for very hygroscopic bodies, but where quick- 
acting balances are used, scarcely necessary for a powdered 

mineral. 

The residue from the moisture determination is brought into 
a platinum crucible and gradually heated to full redness over a 
bunsen, and then ignited over the blast-lamp. This operation is re- 
peated after weighing until a constant weight is obtained. The loss 
(after deducting the percentage of carbon dioxid as found in 
another portion) may be taken as water and organic matter. 
This method is sufficient for all practical purposes, but when 
minerals containing fluorin are strongly ignited, a part of the 
fluorin is expelled; hence, if more accurate determinations are 
required, the loss of fluorin must be taken into account. It has 
been proved that a pure calcium fluorid undergoes progressive 
decomposition at a bright red heat with formation of lime. 

IQ5 Carbon Dioxid.— Many forms of compact apparatus have 
been devised for this estimation, but none of them is more satis- 
factory than Knorr's apparatus, described in Volume I. Many 
phosphates nnist be heated to the boiling point with dilute acid 
to effect complete decomposition of the carbonates. The dis- 
tillation method described by Gooch is excellent, and when 
once the apparatus is set up its work will be found to be rapid 
and satisfactory.®^ 

Wyatt regards the estimation of carbon dioxid as one of the 



^"^ Phosphates of America, 4th Edition, 1892 : 144. 
""^ U. S. Geological Survey, Bulletin 47, 1SS8 : 16. 



8 






1 



m 



^26 



AGRICUIvTURAL ANALYSIS 



LOSS OF SILICA AND FLUORIN 



227 



\lf 



I 



most important for factory use. The carbonates present in a 
sample indicate the loss of an equivalent amount of acid in the 
process of conversion into superphosphate.^* , 

The apparatus employed for estimating carbon dioxid may be 
any one of those in ordinary use for this purpose. The principle 
of the process depends on the liberation of the gas with a mineral 
acid, its proper desiccation, and subsequent absorption by a caustic 
alkali, best in solution. The methods described for soils in Vol- 
ume I are generally applicable to this class of materials. 

The weight of the sample should be regulated by the content 
of carbonate. When this is very high, from one to two grams 
will be found sufficient ; when low, a larger quantity must be used. 
Hydrochloric is preferred as the solvent acid. Those forms of 
apparatus which are weighed as a whole and the carbon dioxid 
determined by reweighing after its expulsion, are not as reliable 
as the absorption apparatus mentioned. 

196. Soluble and Insoluble Matter. — To determine the insolu- 
ble and by difference the soluble and volatile contents of a min- 
eral phosphate, five grams of the finely ground phosphate are ])u: 
into a beaker, 25 cubic centimeters of nitric acid (specific gravity 
1.20), and 12.5 cubic centimeters of hydrochloric acid (specific 
gravity 1.12) are added. The beaker, covered with a watch- 
glass, is placed ui)on the water bath for 30 minutes. The con 
tents of the beaker are well stirred from time to time, and at the 
end of the period the beaker is removed from the bath, filled with 
cold water, well stirred, and allowed to settle. The solution is 
filtered into a half-liter i1ask, and the residue is thoroughly 
washed with cold water, partially dried, and then ignited (finish- 
ing with the blast-lamp), and brought to constant weight. The 
figures thus obtained will, however, be incorrect, because the 
fluorin liberated during the solution of the phosphates dissolves 
a portion of the silica. Hence the results are too low. Never- 
theless, as the same action would occur in the manufacture of a 
superphosphate from the same material, the determination may 
be considered as a fair approximation to commercial practice. 
The ignited residue must be tested for phosphorus pentoxid. 

^* Phosphates of America, 4th Edition, 1892 : 145. 



197. Treatment of the Solution.— The flask containing the 
filtrate is filled to the mark with cold water, and the solution 
is thoroughly mixed by twice pouring into a dry beaker and 
returning to the flask. Cold water is used for washmg the res^ 
idue since if hot water be used, the sesquichlorids are apt to 
become basic and insoluble, and hence to remain in the residue 
and on the filter paper. Besides, as the flask is to be filled to the 
mark the contents must be cold before any volumetric measure- 
ments can be made. The solution may then be used for the 
general determination of the dissolved matters therein. 

198. Silica and Insoluble Bodies.— Wyatt describes the follow- 
ing method for determining the total insoluble or siliceous matters 
in a mineral phosphate.«^ Five grams of the fine sample are 
placed in a porcelain dish with about 30 cubic centimeters of 
aqua regia. The dish is covered with a funnel, placed on a sand 
bath, and, after solution is complete, evaporated to dryness with 
care to prevent spluttering. When dry, the residue is moistened 
with hydrochloric acid and again dried, rubbing meanwhile to a 
fine powder. The heat of the bath is then increased to 125° 
and maintained at this temperature for about 10 minutes. When 
cool, the residue is treated with 50 cubic centimeters of hydro- 
chloric acid for 15 minutes. The acid is then diluted and fil- 
tered on a gooch, which is washed with hot water until the filtrate 
amounts to a quarter of a liter. The residue in the crucible 
is dried, ignited and weighed. Unless the solution be subse- 
quently boiled with nitric acid, all the phosphoric acid may not 

be retained in the ortho form. 

199. Loss of Silica and Fluorin— It is difficult to estimate 
the total silica by the ordinary methods of mineral analysis. This 
is due to the fact that in an acid solution of a substance con- 
taining silicates and fluorids the whole of the silica or the fluorin, 
as the case may be, may escape as silicofiuorid on evaporation. 
Again, it is not easy to decompose calcium phosphate by fusing 
with sodium carbonate. If an attempt be made to do this, how- 
ever, the process should be conducted as follows : A portion of 
the sample is ground to an impalpable powder in an agate mor- 
tar. From one to two grams of the substance are mixed with 

^ Phosphates of America, 4th Kdition, 1892 : 147. 






228 



AGRICULTURAL ANALYSIS 



LIME METHOD OF IMMENEXDRFF 



229 



111 



^^ 



five times its weight of sodium carbonate and fused with the 
precautions given in standard works on quantitative analysis. 
The fused mass is digested in water, boiled, and filtered, and the 
residue washed first with boiling water and afterwards with am- 
monium carbonate. The filtrate contains all the fluorin as sodium 
fluorid, and, in addition to this, sodium carbonate, silicate and 
aluminate. The filtrate is mixed with ammonium carbonate and 
heated for some time, replacing the ammonium carbonate which 
evaporates. The silicic acid and aluminum hydroxid which are 
formed, are separated by filtration and washed with ammonium 
carbonate. To separate the last portions of silica from the fil- 
trate, add a solution of zinc oxid in ammonia. Evaporate until 
no more ammonia escapes and separate by filtration the zinc 
silicate and oxid. Determine the silica in this precipitate by dis- 
solving in nitric acid, evaporating to dryness, taking up with 
nitric acid and separating the undissolved silica by filtration. 
In the alkaline filtrate the fluorin mav be estimated bv the usual 
method as calcium salt. 

200. Estimation of Lime. — The following is the Glaser-Jones 
method, as practiced ])y Chatard in the Geological Survey:'''^ 
One hundred cubic centimeters of the solution (containing one 
gram of the original substance) are evaporated in a beaker to 
about 50 cubic centimeters; 10 cubic centimeters of dilute sul- 
furic acid (one to five) are added; and the evaporation is con- 
tinued on the water bath until a considerable crop of crystals 
of gypsum has formed. The solution is allowed to cool, when 
it generally becomes pasty, owing to the separation of additional 
gypsum, and 150 cubic centimeters of 95 per cent, alcohol are 
slowly added, with continual stirring, and the whole is allowed 
to stand for three hours, being stirred from time to time, filtered, 
with the aid of a filter-pump, into a distillation flask, and the 
crystalline precipitate washed witli 95 per cent, alcohol. The 
filter, with the precipitate, is removed from the funnel and in- 
verted into a platinum crucible, so that, by squeezing the point 
of the filter, the precipitate is made to fall into the crucible, and 
the paper can be pressed dow^n smoothly upon it. On gentle 

^* Transactions of the American Institute of Mining Kngineers, 1892-93, 
21 '. 168. 



1 

" I 

»■■* 



heating of the crucible, the remaining alcohol burns off ; and when 
the paper has been completely destroyed, the heat is raised to the 
full power of a bunsen for about five minutes. After cooling in 
a desiccator the crucible containing the calcium sulfate is w^eighed. 
The filtration may also be accomplished on asbestos felt. 

201. The Ammonium Oxalate Method. — This method has 
been extensively used in this country in commercial work, and is 
carried out as described by Wyatt."' The total filtrates from the 
iron and alumina precipitates, secured as described in paragraph 
196, are well mixed and concentrated to a volume of about 100 
cubic centimeters. There are added about 20 cubic centimeters 
of a saturated solution of ammonium oxalate, and, after stirring, 
the mixture is allowed to cool and remain at rest for six hours. 
The supernatant liquid is poured through a filter, the residue 
washed three times by decantation with hot water and brought 
upon the filter. The beaker and precipitate are washed at least 
three times. The precipitate is dried and ignited at low redness 
for TO minutes. The temperature is then raised by a blast and 
the ignition continued for five minutes longer, or until the lime 
is obtained as oxid. The precipitate is likely to contain some 
magnesia. The magnesia is estimated in the filtrates from the 
lime determination by first mixing them and concentrating to 
100 cubic centimeters, wdiich, after cooling, are made strongly 
alkaline with anmionia. After allowing to stand for 12 hours, 
the ammonium magnesium phosphate is collected and reduced 
to magnesium pyrophosphate by the usual processes. If one 
gram of the original material has been used, the pyrophosphate 
obtained, multiplied by 0.36, will give the weight of magnesia 
contained therein. 

202. Lime Method of Immendorff. — The tedious processes 
required to determine the lime in the presence of iron, alumina, 
and large quantities of phosphoric acid are well known to ana- 
lysts. Immendorff has published a method, accompanied by ex- 
l)erimental data, based on the comparative insolubility of cal- 
cium oxalate in a very dilute solution of hydrochloric acid. He 
has shown in the data given that the lime is all precipitated in 
the conditions named and that the precipitate, when properly pre- 

" Phosphates of America, 4th Edition, 1892 : 153. 



%l 



\ 



230 



AGRICULTURAL ANALYSIS 



THE ACETATE METHOD 



231 



pared, is not contaminated with weighable amounts of the other 
substances found m the original sokition.**^ The ease with which 
oxahc acid can be determined vokmietrically with potassium per- 
manganate sokition aids greatly in the time-saving advantages 

of the process. 

In a hydrochloric acid solution of a mineral phosphate an 
aliquot part of the filtrate representing about 250 milligrams of 
calcium oxid, usually about 100 cubic centimeters, is used for 
the analysis. Ammonia is added in slight excess and then the 
acid reaction restored with hydrochloric until shown plainly by 
litmus. The solution is then heated and the lime thrown down 
by adding a solution of ammonium oxalate in excess. In order 
to secure a greater dilution of the hydrochloric acid after the 
precipitation has been made, water is added until the volume is 
half a liter. Before filtering, the whole is cooled to room tem- 
perature. The precipitate is washed first with cold and after- 
wards with warm water. The well washed precipitate is dis- 
solved in hot dilute sulfuric acid and the solution, while hot, 
titrated with a standard solution of potassium permanganate set 
by a solution of ammonio-ferrous sulfate. 

If one cubic centimeter of the permanganate represent 0.007 
gram of iron it will correspond almost exactly to 0.0035 -gram of 
calcium oxid. The presence of iron in the original solution does 
not seem to affect the results. 

Example. — Sample of mineral phosphate, f\\t grams in half a 
liter. Strength of potassium permanganate, one cubic centimeter,, 
equivalent to 0.00697 gram of iron and to 0.003484 gram of 
calcium oxid. 

Twenty-five cubic centimeters of the solution, representing one 
quarter of a gram, in which the lime was precipitated as above 
described, required 38.4 cubic centimeters of the potassium per- 
manganate to saturate the oxalic acid. Then 38.4X0.003484= 
0.133786 gram, or 53.51 per cent, of calcium oxid. The method 
is also ap])licable to basic slags. 

203. Estimation of Iron and Alumina in Mineral Phosphates. 
— When nnncral phosphates arc to be used for the manufacture 

*" Die laiuhvirlschaftlichen Ver.suchs-Stationen, 1887, 34 : 379. 



"'$. 



of superphosphates by treatment with sulfuric acid their content 
of iron and alumina becomes a matter of importance. By reason 
of the poor drying (jualities of the sulfates of these bases their 
presence in any considerable excess of a few per cent, becomes 
exceedingly objectionable. The quantity of sulfuric acid re- 
quired for the formation of the sulfates is also a matter of 
economic importance. The accurate estimation of these ingre- 
dients is not only then a matter of scientific interest, but one of 
great commercial significance to the manufacturer. 

The conventional methods so long in use depending on the 
precipitation of the iron and alumina as phosphates in the pres- 
ence of acetic acid have been proved to be somewhat unreliable. 
Not only does the acetic acid fail to prevent the precipitation of 
some of the lime, but it also dissolves more or less of the iron 
and aluminum phosphates: The solution of the precipitate and 
its reprecipitation by the addition of ammonia, may free the sec- 
ond preci])itate from lime, but it increases the error due to the 
solubility of the aluminum salt. The methods recently introduced 
for the estimation of iron and alumina in presence of excess of 
lime and phosphoric acid are not entirely satisfactory, but are the 
best which can now be offered. 

204. The Acetate Method. — The principal of this process is 
based on the fact that in a solution containing iron, alumfna, 
lime and ])hosphoric acid, the iron and aluminum phosphates can 
be thrown down in a slightly acid solution by ammonium ace- 
tate while the calcium phosphate remains in solution. The acidity 
in the older methods is due to acetic and can be secured by making 
the solution slightly alkaline with ammonia and adding acetic to 
slight acidity. One of the methods of conducting the operation 
is that of C. Glaser.^^ This modification of the older i)rocesses is 
based on the assumption that at 70° the iron and aluminum phos- 
phate is ([uantitatively precipitated by ammonium acetate in a 
dilute solution containing no free chlorin and that the mixed 
precipitate of iron and aluminum phosphates obtained at this 
temperature is free of lime. The operation is conducted in the 
following manner: 

The hydrochloric acid solution of the phosphate must contain 
^ Zeitscbrift fiir analytische Chemie, 1892, 31 : 3^3- 



^ 



232 



AGRICULTURAL ANALYSIS 



if 

) ■-■'! 
s ■: if 

illi 



' ;; J 



vi.i 






til 



:S 



no free chlorin and is treated with a few drops of methyl orange 
solution. Ammonia is added until nearly neutral, but the acid 
reaction is retained, as shown by the indicator. A few cubic cen- 
timeters of ammonium acetate are added, which produce a yellow 
coloration of the liquid and also a complete precipitation of the 
iron and aluminum phosphates when warmed to 70°. At this 
temperature the precipitation of any calcium phosphate is avoided. 
A small quantity of the lime may be carried down mechanically 
and therefore the precipitate should be dissolved in hydrochloric 
acid and the precipitation again made as above after the addi- 
tion of some sodium phosphate. If the original solution contains 
any free chlorin, as may be the case when aqua regia is employed 
as solvent, before beginning the separation, ammonia should be 
added in slight excess and the acidity restored by hydrochloric 
after adding the indicator. In washing the precipitates, water of 
not over 70° must be used. As has been shown by Hess in the 
work cited in the next paragraph, the statement that the precipi- 
tates obtained as above are free of lime has not been proved to 
bt' strictly correct. The process, however, is a distinct improve- 
ment over the older methods and forms the basis of the amended 
process given below, which appears to be sufficiently accurate to 
entitle the acetate method to favorable consideration. ^ 

205. Method of Hess. — Hess has made an investigation of the 
standard methods of determining iron and aluminum oxids in the 
presence of ])hos])h()ric acid and has shown that the assumption, 
that the composition of the precipitate is represented by the form- 
ula Al,(PO,).+Fe,(P04)o, is erroneous."'^ 

In the washing of the precipitated iron and aluminum phos- 
phates, there is a progressive decomposition of the compound 
with the production of the basic salt. The composition of the 
precipitate at the end is dependent chiefly upon the way in 
which the washing takes place. It is quite difficult to always 
secure a washing in exactly the same way, and the final composi- 
tion of the precipitate varies with almost every determination. 
It is not, therefore, an accurate proceeding to take half the 
weight of the precipitate as phosphoric acid or as iron oxid and 

^ Zeitschrift fiir angewandte Chemie, 1894, 7 : 679, 701. 



METHOD OF HESS 



233 



alumina. In every case it is necessary to dissolve the precipi- 
tate and determine the phosphoric acid in the regular way. 
Hess proposes the following method for carrying out the acetate 
process of separation : 

The mineral phosphate should be dissolved in hydrochloric 
acid and the solution made up to such a volume as shall contain 
in each 50 cubic centimeters one gram of the original sub- 
stance. This quantity of the solution is diluted with two or 
three times its volume of water to which a drop of methyl orange 
solution (1:100) is added, and ammonia added with constant 
stirring until the solution is just colored and still reacts slightly 
acid. Without taking any account of the precipitate which is 
produced by this approximate neutralization of the solution, there 
are added 50 cubic centimeters of acid ammonium acetate which, 
in one liter, contains 250 grams of commercial ammonium acetate. 
The acidity of the solution is due to an excess of acetic in the 
commercial salt. The temperature is carried to 70° and the pre- 
cipitate produced immediately separated by filtration, washed 
four times with water below 70°, and again dissolved in dilute 
hydrochloric acid. The solution is mixed with 10 cubic centi- 
meters of a 10 per cent, ammonium phosphate solution and again 
almost neutralized as described above, and 25 cubic centimeters 
of the ammonium acetate solution added and warmed to 70". 

The precipitate obtained is once more dissolved and precipita- 
ted as above described, and is then collected upon a filter, washed 
ignited and weighed. The residue after ignition is dissolved in 
the crucible by heating with a little concentrated hydrochloric 
acid, and washed into a beaker. Any silicic acid present is sepa- 
rated by filtration, ignited, weighed, and subtracted from the 
total weight of the precipitate. To the filtrate is added ammonia 
to diminish the acidity, but not sufficient to produce a precipitate, 
and the clear solution is mixed with 30 cubic centimeters of the 
ordinary ammoniacal citrate solution and 15 cubic centimeters of 
magnesium mixture, and the precipitation of the ammonium mag- 
nesium phosphate hastened by stirring with a glass rod. 

It is advisable to make the filtrate from the third precipitation 
slightly ammoniacal and to boil it for a long time. If the opera- 



in 

It '' 



f '1 



ii 






! f' 






■I 



I 



Ii 



234 



AGRICULTUIL^L ANALYSIS 



lion has been carried on correctly, there occurs only a slight pre- 
cipitate of C3i^l\(J^ amounting only to a few milligrams. In 
some cases it may be necessary to dissolve the precipitate and 
reprecipitate the iron and aluminum phosphates a fourth time. 

The whole time recpiired for the triple precipitation, according 
to Hess, if all the operations be properly conducted, is from 
three to four hours. It is therefore possible by this variation of 
the acetate method to secure a determination of the iron and 
alumina as phosphates in the same time which is occupied by 
the Glaser-Jones method, when the separation of iime is taken 

into account. 

If the solution of the mineral phosphate employed contains any 
notable quantity of organic material, it must be destroyed by 
boiling with bromin or some other oxidizing agent, before the 
preciiMtation by the acetate method is commenced. 

The presence of silicic acid need not be taken into special con- 
sideration since this can be detected and determined in the phos- 
phate precipitates after they have been ignited and weighed. 
The determinations of the phosphoric acid were made by direct 
precipitation with ammonium in the presence of citrate; they 
agreed perfectly with the previous precipitations with molybdic 
solution. 

206. Method of Eugen Glaser. — The principle on which this 
method rests, depends on the ])reliminary removal of the lime by 
conversion into calcium sulfate and its precipitation in the presence 
of strong alcohol.^^ This process does not require the use of 
acetic acid which in the old method dissolved more or less of the 
aluminum ])li()sphate, thus introducing errors of considerable 
magnitude in those cases where the mineral phosphates contained 
notable quantities of alumina. It is conducted as follows: 

Five grams of the phosphate are dissolved in a mixture of 
25 cubic centimeters of nitric acid of T.2 specific gravity and 
about 12.5 cubic centimeters of hydrochloric acid of 1.12 specific 
gravity, made up to a volume of half a liter, and filtered. One 
hundred cubic centimeters of the filtrate, ecpuvalent to one gram 
of the substance, are placed in a quarter-liter flask and 25 cubic 

*' Zeitschrift fiir angewandte Chemie, 1889, 2 : 636. 



DIFFICULTIES OF THE GLASER-ALCOHOL METHOD 235 

centimeters of sulfuric acid of 1.84 specific gravity added. The 
flask is allowed to stand for about five minutes and meanwhile 
shaken a few times. About 100 cubic centimeters of 95 per cent, 
alcohol are added and then the flask is filled with alcohol to the 
mark and well shaken. A certain degree of concentration takes 
place, and this is compensated for by lifting the stopper and filling 
again with alcohol to the mark and shaking a second time. After 
allowing to stand for half an hour the contents of the flask are fil- 
tered, and 100 cubic centimeters of the filtrate, equal to four-tenths 
gram of the substance, evaporated in a platinum dish until the 
alcohol is driven ofif. The alcohol-free residue is heated to boil- 
ing in a beaker with about 50 cubic centimeters of water. Am- 
monia is added to alkaline reaction, but in order to avoid strong 
effervescence it is not added during the boiling. The excess of 
ammonia is evaporated, the flask allowed to cool, the contents 
filtered, precipitate and filter washed with warm water, dried, 
ignited and the phosphates of iron and alumina weighed. Half 
of the weight of the precipitate represents the weight of FcsOg 
-f ALO3. The estimation, as before indicated, should be carried 
en without delay, the whole time required not exceeding from 
one and a half to two hours. 

. 207. Difficulties of the Glaser-Alcohol Method. — The objections 
on the part of English chemists to the method of freeing dis- 
solved phosphate from lime by means of alcohol preparatory to- 
the separation of iron and alumina are as follows :^^ 

1. To w^orking upon a solution representing as little as 0,4 
gram of phosphate. 

2. To employing nitro-hydrochloric acid as the solvent for the 
raw phosphate and consequently to including in the oxids of 
iron and alumina any iron previously present as pyrite. 

3. To the plan of dividing the phosphates of iron and alumina 
found by two to obtain the oxids of iron and alumina, instead of 
<letermining the phosphoric acid in the precipitates and deducting 
its weight from the total. 

4. Should the phosphate under examination contain magnesia, 
the phosphates of iron and alumina obtained in the foregoing 

^'' Shepherd, Chemical News, 1891, 63 : 251. , 



i 



236 



AGRICUIvTURAL ANALYSIS 



I ■ ! ■ ' I 



' Mi 
If ,;a 



M 



; t 



process must be freed from this impurity by removing tlie precipi- 
tate from the filter, boihng with water and a little nitrate of am- 
monia and repeating this treatment, if after the first application 
of it, the filtrate still shows the presence of magnesia. 

208. Jones' Variation.— The method of E. Glaser described 
above, has been found by Jones to be inaccurate on account of 
the alcohol not being added in sufficient quantity in the pre- 
cipitation of calcium sulfate and for the additional reason that the 
amount of sulfuric acid added is more than is actually necessary .^^ 
A further objection to the method is found in the small quantity 
of the original material, viz., 0.4 gram, which gives only a small 
precipitate of iron and alumina, especially in those cases where 
the samples contain only small quantities of these substances. 
Jones modifies the method as follows : Ten grams of the material 
are dissolved in nitro-hydrochloric acid and the solution made up 
to 500 cubic centimeters and filtered. Fifty cubic centiYneters of 
this solution, representing one gram, are evaporated to 25 cubic 
centimeters and, while still hot, 10 cubic centimeters of dilute 
sulfuric acid (one to five) added. The mixture is well stirred 
and 150 cubic centimeters of 95 per cent, alcohol added and, 
after stirring, the solution is allowed to stand three hours. The 
calcium sulfate is collected on a filter, washed with alcohol, and 
the fihrate and washings collected in an erlenmeyer. The wash- 
ing is completed when the last 10 drops, after dilution with an 
equal volume of water, are not reddened with a drop of methyl 
orange. The filtration is conveniently hastened by a moderate 
vacuum. 

The moist calcium sulfate is transferred to a platinum cruci- 
ble, the filter placed on it, the alcohol burned ofif, the filter inciner- 
ated, and the calcium sulfate ignited and weighed. The precipi- 
tate is not sufficiently hygroscopic to ofiFer any difficulties to con- 
ducting the operations in an open dish. The contents of the flask 
are heated to expel the alcohol, which is contaminated with hydro- 
chloric or nitric acid and can not be used again until distilled over 
an alkali. The residue is washed into a beaker, made slightly 
alkaline with ammonia, and again heated till all the ammonia is 

*' Zeitschrift fiir angewandte Chemie, 1891, 4 : 3. 



IRON AND ALUMINA IN PHGSPHATI'S 



237 



driven oflF. This treatment is necessary to prevent the iron phos- 
phate precipitate from being contaminated with magnesia. The 
precipitate is collected on a filter, washed four times with hot 
water, or water containing neutral ammonium nitrate, dried, 
ignited, and weighed. One-half of the weight of the precipitate 
represents the weight of the ferric and aluminic oxids. The 
magnesia is thrown out of the filtrate by saturation with ammonia 
and allowing to stand 12 hours. The phosphoric acid, alkalies 
and sulfuric acid are determined in the original sample by the 
usual methods. Jones' variation of the E. Glaser method has 
been generally approved by experience and is to be recommended 
m general in place of the original process.®* . 

209. Estimation of Iron and Alumina in Phosphates by Crispo's 
Method. — The phosphate of ferric iron is subject to a slight de- 
composition in presence of both hot and cold water with a ten- 
dency to the production of basic compounds. It is soluble to a 
slight extent in hot and cold acetic acid, almost insoluble in am- 
monium acetate, and quite insoluble in ammonium chlorid and 
nitrate. Aluminum phosphate is likewise soluble, to a slight de- 
gree, in acetic acid and ammonium acetate, and insoluble in am- 
monium chlorid and nitrate. The method of Crispo, as practiced 
in the laboratory at Antwerp, for the separation of iron and alu- 
mina in phosphates is based on the above properties.®'^ Five grams 
of the mineral phosphate are dissolved in 500 cubic centimeters 
of aqua regia, containing 40 cubic centimeters of hydrochloric 
acid of 1. 10, and 10 of nitric acid of 1.20 specific gravity. To 50 
cubic centimeters of the filtered solution are added two of 
ammonia (0.96) and 50 of a half-saturated solution of ammo- 
nium chlorid, and the whole boiled. The liquid should remain 
clear, but if it becomes cloudy add a little dilute nitric acid, drop 
by drop, until the turbidity is removed, and then 10 cubic cen- 
timeters of a saturated solution of ammonium acetate, boil for 
three minutes, cool, and filter. The precipitate is washed twice 
with a 10 per cent, solution of ammonitun chlorid and redis- 
solved with two cubic centimeters of nitric acid, and the filter 

*** von Griiber, Zeitschrift fiir analytische Chemie, 1891. 30 : 206. 
"^ First International Congress of Applied Chemistry, Brussels, 1894, 
Proceedings : 20. 



238 



AGRICULTURAL ANALYSIS 



VARIATION OF MARIONI AND TASSELLI 



239 



II 



Pi 



washed with hot water. The phosphoric acid is separated by 
40 cubic centimeters of molybdate solution, and the precipi- 
tate washed three or four times with a one per cent, nitric acid 

solution. 

To the filtrate are added 50 cubic centimeters of a half- 
saturated ammonium chlorid solution, ammonia is added m 
slight excess to produce precipitation and the mixture boiled for 
a few minutes. After filtering, the precipitate is washed with hot 
water three or four times, dissolved in two cubic centimeters of 
nitric acid, and the filter washed with hot water. Again, 50 
cubic centimeters of half-saturated ammonium chlorid solution 
are added and the precipitate thrown down once more by ammo- 
nia in slight excess. The precipitate is washed with hot water 
and finally ignited and weighed as iron and aluminum oxids. 

According to Crispo, the original Glaser method, with its 
various modifications, is not to be considered reliable, and the 
choice lies between the molybdate method as usually practiced, 
and his own for the accurate estimation of iron and alumina. 
Manganese disturbs the accuracy of the results unless the direc- 
tions given are carefully followed. .Manganese phosphate is 
soluble at all temperatures below 50. If then the mixture of 
the phos])hates be allowed to cool before filtering, the iron and 
aluminum salts are not contaminated with manganese. This 
method of Crispo is somewhat tedious, but it is claimed that these 
variations render it exact in respect of the determination- of iron 

and alumina. 

■ 210. Variation of the Alcohol Method. — Chatard conducts the 
(ilaser-Jones process as follows :^^ The distillation flask contain- 
ing the alcoholic filtrate is connected with its condenser and 
heated on a water bath until no more alcohol comes over. This 
distillate, if mixed with a little sodium carbonate and redistilled 
over quicklime, can be used over and over again, so that the ex- 
pense for alcohol is really very slight, while in the use of the 
Glaser method, with its large amount of sulfuric acid, all the 

alcohol is lost. 

When the distillation is ended the residue in the flask is 
»<^ Transactions of the American Institute of Mining Kngineers, 1892-93, 
21 : 169. 



washed into a platinum dish and evaporated to a small bulk on 
the water bath. The dark brown color produced is due to the 
presence of organic matter and this must be destroyed, as it pre- 
vents the complete precipitation of the phosphate in the subse- 
([uent operation. ' 

The organic matter is best destroyed by removing the dish 
from the bath, adding a small quantity of pure sodium nitrate, 
and heating very carefully over the naked ilame, keeping the 
dish well covered with a watch-glass to avoid spattering. The 
mass fuses to a colorless, viscous liquid, becoming glassy when 
cooled and is readily soltible in a hot, very dilute solution of 
nitric acid. The solution transferred to a beaker is made dis- 
tinctly alkaline with ammonia and carefully neutralized with 
acetic acid, diluted with hot water, boiled, and the precipitate of 
iron and alumina phosphates allowed to settle, after which it is 
separated by filtration. 

After the precipitate has been completely transferred to the 
filter, the washing is completed with a dilute solution of ammo- 
nium nitrate. The precipitate is dried, ignited, cooled, ancj 
weighed. 

The determinations should be made in pairs, and one of the pre- 
cipitates used for the estimation of phosphoric acid, by fusing with 
a little sodium carbonate, and the other, after fusion with sodium 
carbonate, is dissolved with sulfuric acid and the iron reduced 
and titrated with potassium permanganate solution. The fil- 
trate from the iron and alumina determination is evaporated 
to a small bulk, made strongly ammoniacal and allowed to stand 
for some time, when the magnesia present separates as ammonium 
magnesium phosphate, which is determined in the usual way. 

If, during the evaporation of the filtrate, any flocculent matter 
vSeparates, it should be removed by filtration and examined before 
precipitating the magnesia. 

211. Variation of Marioni and Tasselli. — The old and classic 
method of separating iron and alumina in the presence of ammo- 
nium acetate has been shown to be subject to errors by Marioni 
and Tasselli in the following respects:®^ ' 

*' Le Stazioni sperinientali agrarie italiane, 1892, 23 : 31. 






r 



240 



AGRICULTURAL ANALYSIS 



METHOD OF KRUG AND MCELROY 



241 



^ 

1;: 






1. The precipitation of a small quantity of calcium phosphate 
with the ferric and aluminum phosphates. 

2. The possible precipitation of basic phosphates if all the 
iron and alumina are not combined with phosphoric acid in the 
mineral. 

3. The partial solubility of ferric and aluminum phosphates 
in dilute acetic acid. 

4. The decomposition of ferric orthophosphate into soluble 
acid phosphate and insoluble basic salt by washing with boiling 

water. 

To avoid these errors the following procedure is proposed: 
From one to five grams of the sample according to its richness 
in phosi)horic aoid is boiled in a flask for 10 minutes with 15 
cubic centimeters of strong hydrochloric acid, and afterwards 
diluted with a double volume of water. A few crystals of potas- 
sium chlorate are added, or several drops of nitric acid, and the 
liquid boiled to expel chlorin. The solution is filtered and the filter 
washed until the volume of the filtered liquid amounts to 150 
cubic centimeters. After cooling, a half -gram of neutral ammo- 
nium phosphate in solution is added, and two cubic centimeters 
of glacial acetic acid, followed by ammonia, drop by drop, until 
a slight precipitate persists on stirring. The mixture is made 
decidedly alkaline by adding ammonia gradually until the alkaline 
reaction is established. Again the same quantity of acetic acid 
is added as above, well shaken, and left for tw^o hours. The pre- 
cipitate is collected on a filter and washed with a 10 per cent, 
ammonium i)hosphate solution. The precipitate is dissolved by a 
minimum quantity of hydrochloric acid and the solution collected 
in the same vessel in which the precipitation took place. A 
second precipitation is conducted just as described above. The 
precipitate is washed as above described and ignited at a dull red 
heat. Half the weight obtained represents the ferric oxid and 

alumina. 

Following these variations, in which the principal novelty is the 
solvent action on the mixed precipitates produced by ammonia, 
by which all are dissolved save the iron and aluminum phosphates, 
the authors claim to get accurate results. 



r -I 



212. Suggestion of Ogil vie.— When a phosphate is dissolved in 
a mineral acid preparatory to the separation of the various sub- 
stances which pass into solution, most authorities advise that the 
solutions be brought to dryness before proceeding to separate the 
calcium. Some analysts, however, neglect this part of the process, 
and, as Ogilvie has shown, with a chance of error.^^ It appears 
from this fact that in the analyses of the majority of the phos- 
phatic products in use for manurial purposes, special care must be 
exercised to procure a pure and perfectly granular precipitate of 
magnesium ammonio-phosphate, either by evaporating the first 
solution to dryness, or by separating the precipitate which forms 
on the addition of ammonia to the solution containing citric acid. 
213. Method of Krug and McElroy.— Krug and McElroy show 
that when sufficient alcohol is added to precipitate all of the cal- 
cium sulfate in the Glaser method, it will also cause a precipitation 
of a considerable quantity of iron, by means of w^hich the calcium 
sulfate will be colored.^'* The presence of potassium and ammo- 
nium salts also affects very notably the precipitation of calcium. 
The procedure suggested, in order to avoid these sources of error, 
is based on the separation of the phosphoric acid by the molyb- 
date method and is as follows : 

One hundred cubic centimeters, equivalent to one gram of the 
substance, in a nitric acid solution, are placed in a half-liter flask 
and a solution of ammonium molybdate added until all the phos- 
phoric acid has been precipitated. The addition of ammonium 
nitrate will hasten the separation of the ammonium phospho- 
molybdate. The liquid should be allowed to stand for 12 
hours. The flask is filled to the mark, the contents well 
shaken, filtered through a dry filter, and duplicate samples of 
200 cubic centimeters each of the filtrate subjected to examination. 
A small quantity of ammonium nitrate is dissolved in the 
liquid, and ammonia cautiously added, keeping the solution as 
cool as possible. The iron and alumina are precipitated as 

»« Crookes, Select Methods in Chemical Analysis, 4th Edition, 1905 : 499. 
^^ Journal of Analytical and Ar^.lied Chemistry, 1891, 5 : 671. 

Zeitschrift fiir an^ewandt* Chemie, 1891, 4 : 170. 243, 357. 

Zeitschrift fiir analytische Chemie. 1S91, 30 : 206. 

Chemical News, 1S91, 63 : 251. 









242 



AGRICULTURAL ANALYSIS 



METHOD OF WYATT 



243 



I 



r.\ 



i ' 






hydroxids. The mixed hydroxids are collected on a filter, washed 
with water, the filtrate and washings being collected in a beaker. 

The precipitate is dissolved with a small quantity of a solution 
of ammonium nitrate and nitric acid, again precipitated with am- 
monia, filtered, washed, ignited, and weighed. This treatment 
is for the purpose of excluding all possibility of error from the 
presence of molybdic anhydrid. After weighing, the mixed oxids 
are fused with sodium bisulfate, the magma dissolved in water, and 
the iron determined volumetrically with potassium permanganate 
after reduction to the ferrous state. 

McElroy has shown later that even the molybdate method of 
separating the iron and alumina from phosphoric acid with the 
improvements as first suggested by Krug and himself, may not 
always give reliable results.^ In a solution containing ferrous 
iron ecjuivalent to 56.4 milligrams of ferric oxid, was placed 
enough of a solution of sodium phosphate to correspond to 100 
milligrams of phosphorus pentoxid. The precipitate was dis- 
solved by adding nitric acid, oxidized with bromin water, and the 
phosphoric acid thrown out with ammonium molybdate. The pre- 
cipitate was washed with weak nitric acid and the combined fil- 
trate and washings neutralized with ammonia. The resultant pre- 
cipitate was dissolved in a solution of ammonium nitrate and nitric 
acid, filtered, and again precipitated with ammonia. In two in- 
stances the quantities of material recovered after ignition were 
56.9 and 57.3 milligrams, respectively, instead of the theoretical 
amount, viz., 56.4 milligrams. 

When the work was repeated after the addition of 400 milli- 
grams of calcium oxid the weight of the ])reci])itate recovered 
was 62.3 and 63.1 milligrams in duplicate determinations. Sim- 
ilar determinations were made with a known weight, viz., 35.6 
milligrams of alumina. The treatment of the mixture was pre- 
cisely as indicated above for iron. The quantity of alumina fin- 
ally obtained was 28.9 and 29.3 milligrams, respectively, in 
duplicate determinations. When the lime was added, however, 
the weights of alumina recovered tv H to 19.8 and 20.6 milligrams 
respectively. These results show that the molybdate metlio<l for 

^ Journal of the American Chemic il Society, 1895, 17 : 260. 



the separation of iron and alumina in the j.resence of a large ex- 
cess of lime and i^hosphoric acid is subject to widely varying 
results, but that the error due to the excess of iron in the weighed 
product is partly corrected by the one due to the deficiency of 
alumina. 

214. Method of Wyatt— A method, formerly very extensively 
used in this country, both hi private laboratories and by fertiliz- 
er factories, for determining iron and alumina is described by 
Wyatt." It is claimed for this method, which is a modification 
of the acetate process, that, while it may not be strictly accurate, 
yet it is rapid and easy, and in the hands of trained analysts 
yields concordant results. Fifty cubic centimeters of the first 
solution of the sample in aqua regia, or an amount thereof equiv- 
alent to one gram of the phosphate, are rendered alkaline by 
ammonia. The resulting precipitate is first redissolved by hydro- 
chloric acid, and then a slight alkalinity is again produced with 
ammonia. Fifty cubic centimeters of strong acetic acid are added, 
the mixture stirred, placed in a cool place and left until cold. 
The precipitate is separated by filtration and washed twice with 
bojling water. The vessel holding the filtrate is replaced by the 
heaker in which the precipitation was made. The precipitate 
is dissolved in a little 50 per cent, hot hydrochloric acid and the 
filter washed with hot w^ater. After rendering slightly alkaline, 
as in the first instance, the treatment with acetic acid is repeated 
as described. The precipitate is w^ashed this time, twice with cold 
water containing a little acetic acid and three times with hot water. 
The precipitate is dried, ignited, and weighed as iron and alumi- 
num phosphate. Half of this w^eight may be taken to represent the 
quantity of iron and aluminum oxids, for all the general purposes 
'of the factory or the control of the daily work at the mines. 

To separate the iron and alumina the ignited precipitate just 
described is dissolved in hot hydrochloric acid, filtered into a 100 
•cubic centimeter flask, and made up to the mark by hot wash- 

v/ater. 

The phosphoric acid is determined in one-half of the filtrate 
•and in the remaining half the iron is reduced with zinc and 

' rhosphates of America, 4th Kdition, 1S92 : 150. 



i! 



244 



AGRICULTURAL ANALYSIS 



IKON AND ALUMINUM PHOSPHATES 



245 






^ 'i 



i^i! 



"! 



deterniined with potassium perniangaiiate in the usual way. 
The phosphoric acid and iron having been thub determined, the 
ahimina is estimated by difference. The chief objection to this 
process is in the excessive quantity of acetic acid used and the 
danger of sohition of the precipitated phosphates caused thereby. 

215. Estimation of the Lime and Magnesia. — The filtrate and 
washings from the first precipitation, (paragraph 213) of iron and 
akimina in the method of Krug and McElroy, above described, 
are collected and sufficient ammonium oxalate is added to precipi- 
tate the calcium. The precipitated calcium is very fine and 
should be collected on a gooch, without pressure. The filtrate 
and washings from the calcium precipitate are again collected, 
and a solution of sodium phosphate added to precipitate the 
magnesia. The solution must be kept cool and slightly alkaline 
with ammonia during the above operations in order to prevent 
the separation of molybdic anhydrid. 

216. Separation of Iron and Aluminum Phosphates from the 
Calcium Compound. — There are many points of difference noted 
in the descriptions given by authors of the deportment of the iron 
and aluminum phosphates in presence of a large excess of the 
calcium salt. Especially is this true of the statements made by 
Hess and Glaser.^ The subject is of such importance, from a 
analytical point of view, as to merit a careful study. 

In the laboratory of the Division of Chemistry a thorough in- 
vestigation of the mutual deportment of these three phosphates 
has been made by Brown with the following results i'* When 
a mixture containing a known weight of the salts is treated exact- 
ly as Hess directs, in no case is there a complete separation of the 
iron aluminum phosphate from the calcium salt. In order to dis- 
cover the cause of the failure, pure solutions of calcium and iron 
aluminum phosphates are treated under identical conditions by 
the necessary reagents. Fifty cubic centimeters of a solution of 
calcium phosphate, containing about one gram of the salt, are 
treated with 100 cubic centimeters of water and 50 cubic centime- 
ters of the commercial ammonium acetate containing 150 grams 

^ Zeitschrift fiir angewaiidle Cheiiiie, 1894, 7 : 679, 701 ; 1889, 2 : 636. 
* Report to Author by W. G. Brown, 1894, 



of the salt in a liter. An immediate precipitate is produced at 
ordinary temperatures, and on heating to (x)"" it becomes abundant. 
The addition of ammonium chlorid, phosphate, and nitrate in suc- 
cessive portions, does not prevent the precipitation. Making 
the solution more dilute lessens the difficulty. When 20 cubic 
centimeters of a 10 per cent, solution of ammonium phosphate 
are first added, followed by the usual quantity of ammonium 
acetate, a clear crystalline precipitate is sometimes observed. 
Experience also shows that the trouble is not due to an excess 
of the ammonium acetate. 

In treating a solution of iron-aluminum phosphate, in similar 
circumstances, with the ammonium acetate, it is found that a 
complete precipitation takes place. 

Since diluting the solution of the calcium salt diminishes its 
tendency to form a precipitate with the ammonium acetate, the 
true method of separation seems to lie in that direction. The 
calcium salt is held completely in solution when the separation 
is made in the following way : 

The solution containing the mixed phosphates is diluted so as 
to contain not more than one gram thereof in halj a liter. To 
this is added one drop of methyl orange, and afterw^ards 
ammonium hydroxid, until a very slight precipitate is formed. 
The mixture is heated to 70° and from 20 to 25 cubic centimeters 
of a 25 per cent, solution of acid ammonium acetate are added, 
enough to change the rose color of the indicator to orange. The 
iion-aluminum phosphate is separated by filtration and washed 
with a hot five per cent, solution of ammonium nitrate. 

The washed precipitate shows no impurity due to calcium, as is 
proved by dissolving it, reprecipitating and filtering, adding 
ammonium hydroxid to the filtrate, and heating for a long time. 
Sometimes a slight troubling of the clear liquid may be observed 
which may be due to a slight solubility of the iron-aluminum 
phosphate in washing, an accident that may occur if the tem- 
perature be allowed to fall below 70°, but no weighable amount 
of material is obtained. If due to calcium phosphate, a greater 
dilution in the first precipitation will remove even this mere trace 
of that salt, in the above conditions the contamination of the 



>1 l* 



I » 



246 



AGRICULTURAL ANALYSIS 



iron-aluniinum precipitate with calcium phosphate may be en- 
tirely avoided. The problem of separating the phosphoric acid 
by the citrate method, followed by a destruction of the citric acid 
in the filtrate by combustion with sulfuric acid according to the 
•kjeldahl process, and final separation of the iron and alumina in 
the residues was already under way when our attention was called 
to substantially the same process described by Jean."^ The meth- 
•cd merits a further critical examination. 

217. Methods of the German Fertilizer Association.— The meth- 
ods of determining phosphoric acid and other constituents in min- 
■eral phosphates according to the directions prescribed by the 
Union of German Fertilizer Manufacturers differ only in unim- 
portant details from other German methods described.^ 
. IVater-SoIitblc Phosphoric Acid,— "This method is applied to 
superphosphate, phosphate j^recipitates and raw phosphates, but 
is not applicable to phosphatic slags. The extraction is performed 
upon 20 grams of superphosphate in a liter flask. The sample is 
•covered with S(X> cubic centimeters of water, shaken for 30 
minutes and filled up to the mark. The ordinary shaking ma- 
<:hine is used. In cases of dotible phosphates they should be pre- 
viouslv boiled with nitric acid in order to convert any pyrophos- 
phate into orthophosphate. It is recommended that the final 
precipitation of the phosphoric acid be conducted according to the 
usual molybdic acid method with only a few unimportant varia- 
tions. 

The Citrate Method. — In lieu of the molybdic acid method the 
Union of German Fertilizer Manufacturers also recommends 
the citrate method, which is carried out as has already been de- 
scribed, with unimportant variations. 

Volumetric Method by Titration idth Uranium Salts. — This 
method, although recognized as being a very old one, is recom- 
mended in cases where there are no large quantities of iron and 
alumina. The method as used does not differ in any marked re- 
pect from that already given. 

Citrate-Soluble Phosphoric Acid. — The method of securing the 

^ Journal de Pharniacie ct de Chiinie, 1895, [6], 1 : 99. 

Chcniisches Central-Hl.itt, 1S95, 1 : 562. 
*"' Methoden ziir Untersuchung der Kunstdiingemittel, 1903 : 2. 



METHODS OF GERMAN FERTILIZER ASSOCIATION 



247 



phosphoric acid which is soluble in a standard solution of citrate 
of magnesia is that of Wagner, which has already been fully 

described. 

Tree Phosphoric Acid. — Two methods are given for determin- 
mg the free phosphoric acid which may be present in a fertilizer. 
The titration method is carried out as follows : The free phosphoric 
acid is extracted with the water-soluble as already described. 
An amount corresponding to one gram of the original substance 
is diluted to about 100 cubic centimeters and two or three drops 
of an aqueous solution of methyl orange made up in the propor- 
tion of one part of pure saU to 100 parts of water added. The titra- 
tion is accomplished by means of soda lye of known strength tmtil 
the red color is converted into yellow. In the standardizing of 
the soda lye a ptire solution of phosphoric acid of known strength 
is used and in about the same dilution as that expected in the 
fertilizer. The change of color takes place immediately when the 
primary salt is formed from the phosphoric acid according to the 
following formula : 

H3P0,+NaH0=NaH.P0,+H,0. 

It is advisable to pass beyond the titration mark in the addi- 
tion of a soda lye ; afterwards separate the ])recipitate by filtra- 
tion and titrate back the excess of alkali with a standard acid in 
an aliquot part of the filtrate. By this method the change of 
color can be more easily recognized. This back titration, how- 
ever, is attended with an error due to the fact that a portion of 
the-excess of soda lye may adhere to the precii)itate and the more 
so in proportion as the amount of excess is greater. A slight 
correction, therefore, should be made, which is determined by ex- 
periments, in order to avoid obtaining too high a content of free 
acid by this method. In the second method the usual gravimetric 
process with molybdate solution is used. 

Estimation of Iron and Alumina. — This is conducted according 
to the method of Glaser and Jones as has already been described. 

Estimation of Pluorin. — For the purpose of determining fluo- 
rin the method of Fresenius and Richters is employed. There are 
two variations of the method, one for raw phosphate and the 
other for superphosphate. Tn the case of a raw phosphate ^\^ 






>l V' 






I 






1 

i 

« 

■1.1 
M 

Pi 



) L 



l\ 



IK 
-11 

1 



i t-:! 






rm 






248 



AGRICULTURAL ANALYSIS 



METHOD 01^ LASNE 



249 



grams are treated in a platinum di->h with 20 cubic centimeters 
of a 20 per cent, acetic acid on a water bath until all the carbonic 
acid is eliminated. The mass is then evaporated to dryness and 
Ignited in order to remove the moisture and any organic substance 
that may be present. The ignited mass is mixed with about 20 
grams of pure ignited quartz sand, then placed in a dry flask of 
about 250 cubic centimeters capacity and treated with 40 cubic 
centimeters of pure concentrated monohydrate sulfuric acid. The 
flask is stoppered in such a way as to connect with it two U-tubes 
filled with water and is then heated for four hours to 140°. 
After the decomj)Osition is completed a stream of warm air 
amounting in all to about one liter is drawn slowly through the 
apparatus. The contents of the U-tubes are poured into a beaker 
and the hydrotUiosilicic acid is treated with one-half-norma'l 
soda-lye, using i)henulphthalein as indicator. In case there are 
only small quantities of fluorin, namely, only one-half of one per 
cent., it is advisable to add some fluorid of calcium of known 
composition and the quantity of fluorin obtained is corrected by 
deducting the added fluorin from the total secured. In the case 
of superphosphate there is added to the five grams of substance 
a sufficient amount of milk of lime to produce a distinct alkaline 
reaction. The mixture is then evaporated and ignited as above. 
After cooling, the mass is rubbed with a pestle and poured through 
a dry funnel into the decomposition flask above mentioned. The 
platinum dish and funnel are repeatedly rinsed with finely ground, 
ignited quartz powder. The rest of the process is carried on as 
has just been described. 

218. French Method for Mineral Phosphates. — Tlie French offi- 
cial methods are adapted to determine phosphoric acid in various 
fomis.^ 

First — Mineral phosphates composed chiefly of dry calcium 
phosphate mixed in a greater or less degree with carbonate of 
lime, silicious materials, etc., and in different degrees of fineness 
as secured by the usual mechanical means. 

Second — Phosphate of fresh bone, phosphate of degelatinized 
bone, animal black, char from the sugar refining factories, etc. 

' Grandeau, Trd\t6 d'Analyse des Mati^res agricoles, 3d Edition, 1897, 
1 : 443- 



Third — Phosphate in products such as farm-yard manure, poud- 
rette, guano, etc. 

Fourth — Phosphates which have been treated by chemical pro- 
cesses producing super])hosphates whether from bone or mmeral 
phosphates, precipitated phosphates, ammoniaco-magnesium phos- 
phates, etc. 

Fifth — Phosphates which are produced in metallurgical opera- 
tions, such as basic slag, etc. 

The methods employed for these various processes are not es- 
sentially different from those which are already described. There 
are certain slight variations in the methods of preparation which 
are of interest but do not introduce any new^ principles or methods 
of procedure. 

219. Method of lasne.^ — With ordinary phosphates, contain- 
ing as much as three per cent, of alumina a convenient quantity 
to use is two grams. If the phosphate be poor in alumina, a 
larger quantity may be employed. The phosphate in a fine powder 
is dissolved in hydrochloric acid with or without the addition of 
nitric acid, as may be desired. The solution is evaporated to 
dryness, moistened several times with hydrochloric acid and 
again dried to render the silica totally insoluble. The soluble 
parts of the residue are taken up in dilute hydrochloric acid 
(one part strong acid to 20 of water) so as not to have more than 
1.5 grams of ITCl to each gram of phosphate. The solution may 
be either filtered and washed or made up to a known volume, fil- 
tered through a dry filter and an aliquot part of the filtrate em- 
ployed for the subsequent analysis. 

A convenient quantity of the filtrate to employ is one which cor- 
responds to 1.25 grams of the original phosphate in case two 
grams have been taken. 

Meanwhile, there should be prepared a solution of five grams 
of caustic soda free of alumina and silica. This is dissolved in a 
nickel dish with about to cubic centimeters of water. The quan- 
tity of soda to be employed is to be calculated as follows : Two 
grams per gram of the phosphate and one gram for each 100 
cubic centimeters of the final volume employed. There is added 

» Bulletin de la Soci^t^ chiinique de Paris, 1896, [3], 15:6, 118, 146, 
237. 



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AGR1CULTU11/\L ANALYSIS 



to the liquor one gram of phosphate of soda containing ahout 20 
];er cent, of phosphoric acid, it is necessary to call attention to 
the fact that the liquor is to contain enough of phosphoric acid 
to completely saturate the lime and that the acid be in excess at 
least one decigram. It will be necessary, therefore, to increase 
a little the (juantity indicated if the phosphate is very rich in car- 
bonate. For certain chalky phosphates, it will be necessary to use 
as much as two grams of the phosphate of soda. 

The soda liquor thus prepared is poured in a fine stream into 
ihe solution of the i)hosphate prepared as above, and its constant- 
ly stirred with a metal spatula. After the addition of the soda, the 
mixture is heated to about 100° for half an hour, but it is pref- 
€rable to prolong the heating for an hour, stirring from time to 
time. After cooling, the mixture is placed in a flask marked at 
250 cubic centimeters, and the volume completed with water to 

the mark. 

To be able to take account of the volume of the precipitate, a 
half cubic centimeter of water, in addition, is added. The mix- 
ture is strongly shaken several times and left for half an hour 
in order to permit the complete ditTusion of the lifiuid through- 
out the precipitate. The contents of the flask are next poured 
upon a dry filter and 200 cubic centimeters of the filtrate cor- 
responding to one gram of the original phosphate, in case two 
grams have been used, employed for the estimation of the alum- 
ina. 

It has been proved that by this treatment all the bases, except 
alumina, which can be present, have been retained as phosphates, 
while the phosphate of alumina has remained completely soluble. 

The 200 cubic centimeters of the filtrate, obtained as above, are 
l^laced in an erlemneyer and hydrochloric acid added until the 
precipitate at first formed is just dissolved. There are then added 
25 cubic centimeters of a solution of ammonium chlorid contain- 
ing 125 grams per liter. Ammonia is then added until there is 
formed a precipitate which persists. The mixture is next heated 
to near ebullition and with great care a solution of dilute ammonia 
is added. The heated mixture should not give off more than a 
feeble odor of ammonia, and it is highly important that the ammo- 



METHOD OF LASNH 



251 



nia be not added in excess. The mixture is then boiled for five 
minutes. It is allowed to rest for some moments and then fil- 
tered still hot. The precipitate is drained upon the filter and the 
filter and the precipitate in the erlenmeyer washed only once. 
The precipitate both on the filter and remaining in the erlen- 
meyer is then redissolved in from 20 to 25 cubic centimeters of 
hydrochloric acid diluted to one-twentieth and heated to lOO^ 
The solution in the erlenmeyer and the wash-waters from the 
filter are united in an erlenmeyer and treated with 3.5 cubic centi- 
meters of a 10 per cent, solution of ammonium phosphate. This 
solution should contain about 53.4 grams of phosphoric acid per 
liter. There is then 0.187 gram of phosphoric acid in 
excess, and this condition should be realized as nearly 
as possible. Ammonia is added until a light precipitate 
persists which is dissolved with great care in a few drops of 
dilute hydrochloric acid, in such a manner that the mixture 
clears up gradually after agitation. This having been accom- 
plished, 1.5 grams of hyposulfite of ammonia are added, or 10 
cubic centimeters of a solution of this salt containing 150 grams 
per liter. The volume of the mixture is completed to about 250 
cubic centimeters, and afterwards it is carried to boiling, which is 
continued 30 minutes, the volume of water being kept up by oc- 
casional additions. At the end of this time the precipitation is 
easily completed. Nevertheless, in order to have a greater cer- 
tainty, there should be added, after suspending the boiling for a 
moment, from four to five drops of a saturated solution of ammo- 
nium acetate. This salt, which in large quantities dissolves phos- 
phate of alumina, has no inHuence in so small a quantity. The boil- 
ing is then continued for five minutes longer. After allowing to 
settle for a few minutes the liquor is filtered still hot. The pre- 
cipitate does not adhere to the walls of the flask and is easily 
collected upon the filter where it is washed seven or eight times 
with boiling water. The collected precipitate, after drying, is 
incinerated and kept at a white heat for 15 minutes in the blow- 
pipe before weighing. The composition of this precipitate is ex- 
actly P20,Al2PO,. The weight of the precipitate multiplied by 
0.418 gives the weight of the alumina therein. 



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AGRICULTURAL ANALYSIS 



ESTIMATION OF ALUMINA AND FERRIC OX ID 



253 



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There is in the second precipitate mentioned above a sHght loss 
of alumina which ])recise experiments have shown me to 
be 0.8 milligranL This is due to a solubility which depends 
only on the volume of the liquid and not upon the weight of the 
precipitate. Eight-tenths of a milligram should, therefore, be 
added to the weight of the alumina as determined above. 

220. Comparison of Methods of Estimation of Iron and Alu- 
mina in Phosphates. — Blattner, in collaboration with Brasseur, at 
Lille, has made a comparative examination of some of the methods 
in use of determining the iron and alumina in natural phosphates. 
They have examined the following processes : 

1. 'I'he process of Maret and I^elattre, which is very extensively 

employed in France. 

2. The method of E. Glaser. 

3. The method of H. Lasne. 

4. The method of J. Grueber. 

The results of their studies are as follows : 

T. 'Hie method of Maret and Delattre gives results which are 
not accurate, the quantities of iron and alumina being usually 
too small. 

2. The method of E. Glaser, embracing separate determinations 
for the oxid of iron and alumina is able to give exact results, 
but if the phosphates contain manganese this substance goes also 
in the precipitate and is counted as alumina, and as a result the 
figures for alumina obtained by the method of Glaser are too high 
when manganese is present. 

3. The method of Lasne gives results which are rigorously exact 
when conducted with reagents which are perfectly pure. It is 
the most exact method known up to the present time, and has been 
tried by the authors in the most minute detail. It can be regarded 
as a standard method. 

4. The method proposed by Grueber appears to be an abridge- 
ment of the method of Lasne. The authors, however, prove that 
it does not give correct results. Grueber applied it to phos- 
phates which were prepared by synthesis and which contained 
only certain of the matters, and not at all, which enter into the 
composition of natural phosphates. Where a great deal of lime 



is present, by the modification of Grueber no alumina at all is 
obtained sometimes, when it may be present to the extent of half 
a per cent. The results of the investigation favor entirely the 
iidoption of the method of Lasne to the exclusion of the others.^ 

221. The Estimation of Alumina and Ferric Oxid in Natural 
Phosphates. — The search for an accurate and rapid method for 
the determination of alumina and iron oxid in the presence of 
phosphoric acid has occupied the attention of analysts for years, 
and many methods have been proposed for this difficult opera- 
tion. It may be said generally that even those methods that 
have stood the tests of extended use have not escaped severe 
•criticism; they are only accurate within narrow and rigidly de- 
fined limits or they are tedious and time-consuming.^*^ 

Aside from its interest from the scientific point of view, this 
sul)ject is of importance in its technical and commercial aspects. 
The value of raw mineral phosphates is judged largely by their 
content of alumina and iron. 

In phosphatic slags the estimation of these oxids is more 
difficult, though possibly not so important. 

Sources of Error in the Older Methods. — The Glaser alcohol, 
the acetate with its various modifications, and the caustic alkali 
methods as carried out by Lasne, Lichtschlag and Gladding, 
have all been criticised and the sources of error pointed out. 

1. In the Glaser alcohol method the precipitation of manganese 
with the iron and aluminum phosphates and the solubility of the 
phosphates in the wash-water are important sources of error. 
Probably the manganese can be eliminated by a second precipita- 
tion in the ])rescnce of a large amount of ammonium chlorid. 
Possibly the presence of a large amount of ammonium sulfate 
may also affect the accuracy of this method, in those cases where 
the excess of ammonia is completely removed by boiling. Alumi- 
rum phosphate is noticeably soluble in a strong sulfate solution, 
which is neutral or faintly acid from SOg. 

2. In the acetate method and its variations there is an error 
•caused by the precipitation of the lime with the iron and alu- 

'^ Cheniiker-ZeiUin^, 1897. 21 : 414. 

'° Veitch, Journal of the American Chemical Society, 1900, 22 : 246. 



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AGRICULTURAL ANALYSIS 



KSTIMATION OF ALUMINA AND FERRIC OXID 



255 



niiniim pliosphates, the solubility of ahiniinuni pliosphatc in cold 
acetate solutions, and the solubility and dissociation of iron and 
aluminum phosphates in water - Also when the phosphates are 
fused with sodium carbonate, and the iron deternuned by pre- 
cipitation with ammonia, the contamination of the iron with 
calcium phosphate, which is not always entirely decomposed by 
fusion, is a source of error. Of these the most serious are the 
first and last mentioned. 

3. In the caustic alkali methods there is danger of some of 
the aluminum bein- held by the voluminous precipitate pro- 
duced bv the alkali ; there is also danger of alumina being pre- 
cipitated if much carbon dioxid is absorbed. Usne and Licht- 
schlag have shown that while the method is long, it gives accu- 
rate results if properly conducted. Blattner and P>rasseur have 
investigated the more important methods and conclude i^^ 

The acetate method should be discontinued^ figures for alum- 
ina are nearly always too low. 

The Olaser method (alcohol) gives accurate results in the 
absence of manganese. 

The caustic soda method, as carried out by Lasne, gives exact 
results. 

In view of these many sources of error in the conventi'^al 
methods, considerable time has been devoted to the study of a 
method that, it is hoped, is free from most of the above men- 
tioned objections. It is an adaptation, so far as possible, of the 
good points of the present best methods. From the precipita- 
ting reagent used, it may be designated the thiosulfate method. 

The use of a soluble thiosulfate for the separation of alumina 
from iron and aluminum from several other metals seems to be 
due to Chancel.^^ Tater it was used by Stead and by Carnot ; 
by the latter for the separation of aluminum as phosphate, in 
the presence of ammonium acetate, from iron.^* Lasne also uses 
it to precipitate aluminum phosphate in the presence of am- 

1' Chemiker-Zeituiig, 1897, 21 : 264. 

^' Bulletin de la Soci^t6 chiniique de Paris, 1897, [3]. 17 : 760. 

>=» Comptes rendus, 1858, 46 : 9^7- 

»* Blair, Chemical Analysis of Iron, 6lh K4-tion, 1901. : 196. •..-• .r 



nionium acetate, after removingiron, lime, etc., with caustic soda. ^'' 
, The thiosulfate has nothing to do with the precipitation, ex- 
cept that it is an exact method of obtaining the desired neu- 
trality. Thomson has devised a method in which he makes use 
of this principle, neutralizing with ammonia and using a delicate 
indicator to determine neutrality.^*' 

Study of the Proposed Method. — One of the first problems pre- 
sented in the study of any method for the determination of 
alumina as phosphate is the composition of the ignited phosphate. 
While there is a general agreement that the normal phosphate 
is only obtained in the presence of an excess of phosphoric acid, 
it is not certain that it is always obtained, even under these condi- 
tions.^^ 

Wash Sohitions. — It seems that the true solution of this prob- 
lem can only be obtained by a study of the solutions used in wash- 
ing the precipitate. Besides waters of all temperatures, solu- 
tions of various salts, such as five per cent, ammonium nitrate, 
ammonium chlorid, one per cent, ammonium nitrate plus 0.02 per 
cent, ammonium phosphate, and dilute ammonium acetate, have 
been proposed and used by many investigators. These various 
washes possibly account for the variations from the normal, so 
fiequently noted. The recently precipitated phosphates of iron 
and aluminum, when freed from adhering salts, are slightly solu- 
ble, or rather are dissociated, in water of any temperature. Those 
who have apparently used water successfully as a w^ash probably 
did not wash enough, only three or four times, to remove the 
adhering salts. Cold ammonium or sodium acetate also slowly 
dissolves aiuniinniii phosphate. 

The effects of the following wash liquors have been studied: 

Water at from 60° to 70° C. 

Five per cent, ammonium nitrate at from 60° to 70° C. 

One per cent, ammonium nitrate at from 60*^ to 70° C. 

Five ])er cent, ammonium nitrate and 0.02 per cent, ammonium 
phosphate at from 60^ to 70° C. 

'•• Bulletin de la Societe chiniique. de PMris.1896. [3], 15 : it8. 
*^ Journal of the Society of Chemical Industry. 1896, 15 : 868. 
'' Cheniiker-ZeitunjT, 1897, 21 : 264. 

Rlair, Chemical Analysis of Iron, 6th Edition, 1906 : 196. 

South Carolina Ai^ricultural Experiment Station, Bulletin 2, 1891. 



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AGRICULTURAL ANALYSIS 



Method of Stmly.— Venous quantities of the pure alumnnini 
sulfate are placedhi a 12-ounce beaker with a solution of two 
.rranis of ammonium phosphate, the resuUing precipitate dis- 
solved in hydrochloric acid, and 25 cubic centimeters of a 50 
per cent solution of ammonium chlorid added. The solution is 
made alkahnc with ammonia and the precipitate just dissolved 
with hvdrochloric acid, noting approximately the number of cubic 
centimeters required after the solution has become acid ; the solu- 
tion is diluted to about 250 cubic centimeters, and for each cubic 
centimeter of hvdrochloric acid added to the acid solution five 
cubic centimeters of a 50 per cent, solution of ammonium thiosul- 
fate were added dropwise, the beaker covered with a watch- 
glass, the solution boiled half an hour, filtered, washed, dried 
and ignited to constant weight. 

■ Washing 20 times with five per cent, ammonium nitrate gives 
practically theoretical results. As many as 50 washings with 
this solution give results slightly low, but still good. The other 
solutions were rejected, as they showed a decided solvent effect, 
except the ammonium nitrates plus ammonium phosphate, upon 
prolonged washing. Twenty washings were required to free the 
precipitate from chlorids, sulfates, and ammonium phosphate. 
In all succeeding work five per cent, ammonium nitrate was used, 
washing 20 times. Tx)ng heating with the blast from 10 to 20 
minutes was required to reduce to constant weight. 

Composition of the J piited Aluminum Phosphate— The phos- 
phoric acid in the aluminum phosphate, washed 20 times witli 
five per cent, ammonium nitrate, was carefully determined by 
precipitation with molybdate solution, washing the precipitate of 
ammonium phosphomolybdate with dilute nitric acid, and wash- 
ing the final precipitate free of chlorids. 
* The salt obtained under the above mentioned conditions seems 
to be the normal phosphate, AIPO4. 

Eifcct of Iron Salts.— V'we grams of ammonium ferric alum 
dissolved in water, two grams of ammonium phosphate added, 
and treated as for aluminum phosphate, precipitating while slight- 
ly warm, washing 20 times with ammonium nitrate, gave aa 









\ t 



ESTIMATION 01^ ALUMINA AND FERRIC OXID 



257 



average of 1.2 milligrams of alumina. The iron, therefore, has 
a slightly disturbing effect when ])rcsent in large quantities. 

Solutions containing aluminum sulfate, ammonium phosphate 
and five grams of ammonio-ferric alum yielded apparently larger 
quantities of alumina, by the usual methods, than the theoretical 
amount. When these solutions, however, were previously treated 
with thiosulfate the theoretical atnounts of alumina were ob- 
tained. 

Effect of Calcium Salts. — The presence of calcium salts pro- 
duces even less disturbance in the results than iron compounds. 
The addition of two grams of calcium phosphate gave no indi- 
cation of alumina in the final results. When aluminum phos- 
phate was present in the same quantity as the calcium salt, the 
theoretical yield of alumina was 74.3 milligrams instead of 70.5 
milligrams, doubtless due to the mechanical entanglement of other 
compounds. When a second precipitation w^as employed, this error 
disappeared. There was obtained an average of 31.5 milligrams 
of alumina where the theoretical yield was 31.9 milligrams. 

From the foregoing results the conclusion seems warranted 
that aluminum phosphate can be quantitatively separated by a 
soluble thiosulfate and ammonium chlorid reagent from a hydro- 
chloric acid solution of iron, alumina, and lime phosphates con- 
taining only a small amount of sulfates. The statement of many 
observers, that theoretical results on aluminum ])hosphates can 
only be obtained in the presence of an excess of phosphoric acid, 
has been confirmed. The error produced by precipitating a sec- 
ond time without adding ])hosphoric acid amounted in some cases 
to two milligrams alumina. 

The Effect of Magnesium, Sodium and Potassium Salts. — Salts 
of sodium, magnesium and potassium were added to the solutions 
containing alumina before precipitation as phosphate, and it was 
found that they exerted no disturbing influence on the results 
obtained. 

The Effect of Sulfates. — In these cases the removal of silica 
is necessary and the property of the insolubility of silica in sul- 
furic acid was used as the basis of separation. The method of 



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AGRICULTURAL ANALYSIS 



Drown was eniploved.^^ W'liile the separation of silica by this 
method is satisfactory, it was found impossible to completely 
precipitate the aluminum phosphate in the presence of a thiosul- 

The presence of more than 1.25 grams of sulfuric acid pre- 
vents the complete precipitation of aluminum phosi)hate, while 
2.75 grams give a decided error. 

The Effect of fluorin.— The presence of a fluorid in a solution 
from which it is attempted to separate aluminum by this method, 
is as disastrous to the results as is the presence of sulfates. 

In none of the current methods is the presence of fiuonn men- 
tioned as a disturbing factor. 

The work so far done shows that alumina can be quantita- 
tively separated as phosphate from a hydrochloric acid solution 
containing aluminum, iron, manganese, lime, magnesium, sodium 
and potassium, when only small quantities of sulfate are pres- 
ent ; that the presence of silica in the solution produces a plus 
error too large to be neglected ; and that the presence of large 
(luantities of sulfates or the presence of fluorids prevents the 
complete precipitation of aluminum phosphate. Therefore, to 
obtain accurate results, silica and fluorin must be removed while 
sulfates, not more than the equivalent of 1.25 grams of sulfuric 

acid, may be present. 

Proposed MetJwd.—Thit following method for estimating alum- 
ina in phosphates is based upon the results of these experiments : 
IVeat one gram of the substance in a platinum dish with from 
five to 10 cubic centimeters of hydrofluoric acid, let stand in the 
cold from two or three hours, heat on the water bath to com- 
plete dryness, add two cubic centimeters of concentrated sulfuric 
acid, running well around the sides, and heat at a low tempera- 
ture until the substance no longer flows in the dish. By this 
process fluorin is completely expelled. Cool and add from 10 
to 20 cubic centimeters of concentrated hydrochloric acid, and 
warm a few minutes to soften the mass; transfer to a small 
beaker, and boil until all aluminum compounds are surely dis- 
solved (from 15 to 30 minutes) : filter from undissolved residue, 
'" Tninsacf ons of tlie American Institute of Mining Engineers, 1878-79, 
7 : 346. 



GENERAL CONCLUSIONS 



259 



if any, washing the filter thoroughly, add 50 cubic centimeters of 
25 per cent, ammonium chlorid solution and ammonia until alka- 
line, then hydrochloric acid until the precipitate just dissolves. 
Cool, dilute to about 250 cubic centimeters, and add 50 per cent, 
sodium thiosulfate solution, drop by drop, until the solution is 
colorless, adding in all 20 cubic centimeters ; cover with a watch- 
glass, boil half an hour, filter, wash back into the same beaker, 
and dissolve in boiling hydrochloric acid ; reprecipitate exactly 
as before, after adding two cubic centimeters of a 10 per 
cent, ammonium phosphate solution. Wash 20 times wath five 
per cent, ammonium nitrate solution, and ignite to constant 
weight. For the second precipitation ammonium thiosulfate may 
also be used, but it is not necessary. 

The greatest difificulty to be overcome in the execution of 
this method in the case of natural phosphates is the error pro- 
duced by the presence of fluorin ; hence it is necessary to heat 
the substance for a long time with sulfuric acid to insure the 
complete removal of fluorin before beginning the separation of 
the aluminum phosphate. 

An attempt to overcome this source of error by adding an 
alkaline acetate before boiling wnth thiosulfate gave no satisfac- 
tory result. 

Estimation of Ferric Oxid. — The determination of ferric oxid 
is made as follows : Dissolve one gram of the substance in 20 
cubic centimeters of sulfuric acid, dilute, filter, washing the filter 
thoroughly, and if any organic matter is present add a little potas- 
sium chlorate and boil until chlorin is expelled. Reduce the iron 
with zinc, filter, and titrate at once with potassium permanganate 
solution, one cubic centimeter of which equals 0.0025 gram of 
ferric oxid. 

222. Separation of Alumina from Iron by Phenylhydrazine. — 
This method of separation was proposed by Hess and Campbell 
and elaborated by Allen. ^^ It is based on the reduction of the 
iron by a sulfite and the precipitation of the alumina by phenyl- 
hydrazine. 

223. General Conclusions. — It is evident from the foregoing 

'® Journal of the American Chemical Society, 1899, 21 : 776. 
Journal of the American Chemical Society, 1903, 25 : 421. 



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AGRICULTURAL ANALYSIS 



that many difficulties beset the separation of iron and aliunina 
from the other substances occurring in phosphatic deposits. Veitch 
has called especial attention to these difficulties in view of the 
persistence with which ordinary precautions are disregarded.-'^ 
The important points to be kept in view are that all the iron 
should be in solution in the ferric state, the solution should be free 
of silica, and should contain no more than 0.5 gram substance in 
300 cubic centimeters. In these conditions the precipi- 
tation of the phosphates of iron and alumina is made in a five 
per cent, solution of ammonium chlorid, and the precipitate after 
washing several times with hot water, is dissolved in hydrochloric 
acid diluted to about 300 cubic centimeters and reprecipitated as 
before, with care to have always an excess of phosphoric acid 
over the amount required to unite with all the iron and alumina 
present. The precipitate is washed free of chlorid with a five 
per cent, ammonium nitrate solution and ignited to constant 
weight. With the precautions noted, concordant results may be 
obtained by precipitating with ammonium acetate and determining 
the phosphates thrown out. The aluminum may be separated 
from the iron with thiosulfate of ammonium or sodium, as pointed 
out by Veitch.-^ The iron may afterwards be determined by 

titration. 

The iron may be determined separately by reduction to the 
ferrous state and oxidizing by potassium permanganate or bi- 
chromate. 

The solutions must in all cases be free of organic matter. If 
manganese titanium or vanadium be present the accuracy of the 
iron determination will be aft'ccted, and these elements must be 
separately determined where extreme accuracy is desired. The 
small c|uantities of these bodies usually found. although they deport 
themselves in the presence of phosphoric acid much in the same 
wav as iron, do not introduce anv material error into the per- 
centage determination when weighed as iron phosphate, because 
thev have apprj^xiniately the same atomic weight as iron itself. 

224. Estimation of Sulfuric Acid. — As a rule, sulfates are not 

20 Proceedin^^ of Ww Fifth International Congress of Applied Chemis- 
try, Berlin, 1903, 1 : 492. 

=" Journal of the American Chemical Society, 1900, 22 : 246. 



SIGNIFICATION OF FLUORIN 



261 



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abundant in mineral phosphates. In case the samples are pyritif- 
erous, however, considerable quantities of sulfuric acid may be 
found after treatment with acjua rcgia. 

The acid is precipitated with barium chlorid, in the usual way, 
in an aliquot portion of the filtrate first obtained. The precipi- 
tate of barium sulfate is washed with hot water until clean, dried, 
ignited, and weighed. If the portion of the filtrate used repre- 
sents half a gram of the original material, then the weight of 
barium sulfate obtained multiplied by 0.6858 will give the quan- 
tity of sulfur trioxid in one gram. 

OCCURRENCE OF FLUORIN IN PHOSPHATES 

225. Signification of Fluorin. — Fluorin is cjuite a constant con- 
stituent of organic ])hosphates of lime, as, for instance, bones and 
teeth, and occurs in considerable quantities in many deposits of 
such phosphates used for commercial purposes. It is the cause 
ofjTiuch discomfort and annoyance in fertilizer factories. 

^The phosphates of pure mineral origin, and also sedimentary 
phosphates, contain uniformly considerable quantities of fluorin, 
in fact, in quite a definite proportion, and generally correspond 
in composition to apatite. Under the infiuence of living organs, 
of plants and animals, the fiuorin tends to disappear.-''^ 

The exact determination of fluorin, therefore, in phosphates, is 
of more than usual interest because its amount will throw much 
light on the origin of the sample under examination. 

Free coproliths, that is, nodules of organic phosphates, are 
very rarely found. What are so called, preserve only the form. 
The original materials have been replaced by the fluoi phosphates 
of more distinctly mineral nature. The fossil bones sometimes 
found in sedimentary phosphate deposits are only bones in form, 
just as fossil trees are only so in form. The analysis of the 
])hosphatic material composing them shows them to he different 
from true bone. Only fossil phosphates unmetamorphosed exist 
in recent geological ei)ochs and in guano deposits. 

T^he almost universal presence of fluorin in natural phosphates 
makes of especial interest the methods for its exact estimation. 
The presence of fluorin is of little consequence from a i)ractical 
'^ Lasiie, L'Engrais, 1896, 11 : 1145. 1168. 



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AGRICULTURAL ANALYSIS 



ii 



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point of view, except in the decomposition of phosphates with 
sulfuric acid, where the evokition of hydrofluoric acid or hydro- 
fluosihcic acid may cause grave inconvenience to the workman 
and damage to the apparatus. It is important to know the exact 
content of a phosphate in fluorin before submitting it to the pro- 
cess of manufacture, by means of which phosphoric acid is ren- 
dered sohible in water and ammonium citrate. The principles 
upon which the estimation of the fluorin depend, comprise both 
the decomposition of the substance by fusion with the carbonate 
of soda and silica, and the estimation of the fluorin in the 
hydrofluosilicic acid evolved by the simultaneous action of con- 
centrated sulfuric acid and silica upon the fluorin compound. The 
last method theoretically leads to the realization of the conditions 
necessary for an exact determination, but in practice it has been 
fcnind to be attended with very great diflkulties. The assump- 
tion that the hydrofluosilicic acid is evolved in the pure state is 
not always correct, since phosphates contain quite commonly 
some carbonates and organic matters, and even chlorids^- When 
these compounds are trtrated with concentrated sulfuric acid, there 
is set free some sulfurous, carbonic, and hydrochloric acids, and 
these escaping in a gaseous form, are likely to carry with them 
also some water vapc^r. In the application of this method it has 
therefore been found necessary to previously ignite the phosphate, 
and this operation is also open to objections. In case calcination 
is practiced, it is necessary to carry it so far that there remains 
no trace of carbonic acid, or of carbon, for the presence of these 
bodies would interfere^ seriously with the subsequent determina- 
tion of the fluorin. ^ Even when this method can be successfully 
])racticed with natural phosphates, it will be found extremely diffi- 
cult of application in the estimation of any residual fluorin in 
superphosphates. ^ 

226. EstimatiT)n of Fluorin by the Method of Berzelius as 
Modified by Chatard.— The method of estimating fluorin as pro- 
posed by IkTzclius has been found quite satisfactory in the labo- 
ratory of the Geological Survey, with the modifications given be- 
low.23 

» Transactions of the American Institute of Mining Engineers, 1892-93, 
21 : 170. 



ESTIMATION OF FLUORIN 



263 



Two grams of the phosphate are intimately mixed in a large 
platinum crucible with three grams of precipitated silica and 12 
grams of pure so(Hum carbonate, and the mixture is gradually 
brought to clear fusion over the blast-lamp. When the fusion 
is complete the melt is spread over the walls of the crucible, 
which is then rapidly cooled (preferably by a blast of air). If 
this has been properly done, the mass separates easily from the 
crucible, and the subsequent leaching is hastened. The mass, 
detached from the crucible, is put into a platinum dish into which 
whatever remains adhering to the crucible or its lid is also washed 
with hot v^ater. A reasonable amount of hot water is now put 
into the dish, which is covered and digested on the water bath 
until the mass is thoroughly disintegrated. To hasten this, the 
supernatant liquid may, after a while, be poured off, the residue 
being washed into a small porcelain mortar, ground up, returned 
to the dish and boiled with fresh water until no hard grains are 
left. The total liquid is filtered, and the residue is washed with 
hot water. The filtrate (which should amount to about half a 
liter) is nearly neutralized with nitric acid (methyl orange being 
used as indicator), some pure sodium bicarbonate is at once 
added, and the solution (in a platinum dish, if one large enough 
is at disposal, otherwise in a beaker) is placed on the water 
bath, wdicn it speedily becomes turbid through separation of 
silica. As soon as the solution is w^arm it is removed from the 
bath, stirred, allowed to stand for two or three hours, and then 
filtered by means of the filter-pump and washed with cold water. 

The filtrate is concentrated to about a quarter of a liter and 
nearly neutralized, as before, some sodium carbonate is added, 
and the phosphoric acid is precipitated with silver nitrate in 
excess. The precipitate is separated by filtration and washed 
with hot water, and the excess of silver in the filtrate is removed 
with sodium chlorid. 

The filtrate from the silver chlorid (after addition of some 
sodium bicarbonate) is evaporated to its crystallizing point, then 
cooled and diluted with cold water ; still more sodium bicarbon- 
ate is added, and the whole is allowed to stand, when additional 
silica will separate, and this is to be removed by filtration. 

This final solution is nearly neutralized, as before ; a little 



1 m 









i 












» i 

111 






't ii 



i 



:fr - 



264 



AGRICULTURAL ANALYSIS 



III 



11 



sodium carbonate s(.lution is added; it is heated to boding and 
an excess of solution of calcium chlorid is added. Ihe precipi- 
tate of calcium tluorid and carbonate must be boded for a few 
minutes, when it can be easily filtered and washed with hot 
water. The precii)itate is then washed from tlie filter into a 
small platinum dish and evaix>rated to dryness, while the filter 
after being partially dried and used to wipe off any particles of 
the precipitate adhering to the dish in which it was formed, is 
burned, and the ash is added to the main precipitate. This, 
when dry, is ignited, and allowed to cool; dilute acetic acid is 
added in excess, and the whole is evaporated to dryness, being 
kept on the water bath until all odor of acetic acid has disap- 
l)eared. The residue is then treated with hot water, digested, 
filtered on a small filter, washed with hot water, partially dried 
put into a crucible, carefully ignited, and weighed as calcium 
lUiorid. The calcium tluorid is then dissolved in sulfuric acid 
])y gentle heating and agitation, evaporated to dryness on a 
radiator, ignited at full red heat, and weighed as calcium sulfate. 
From th'is weight the e(iuivalent weight of calcium fluorid should 
be calculated, and this should be very close to that actually 
found as above, but should never exceed it. The diff:rence 
which is generally about a milligram (sometimes more), is du'j 
to silica precipitated with the tluorid. The ])erc-ntage of fiuorin 
is, therefore, always calculated from the weight of the sidfate. 
and not from that of the tluorid obtained. 

The main inii)rovements in this method are the use of sodium 
bicarbonate to separate the silica, and the keeping of the earlier 
solutions as dilute as possible, which can not be done if ammo- 
nium carbonate be used for tlie se])aration of the silica. These 
changes make the lluorin estimation, although still tedious, far 
more rapid than before, and the results are very satisfactory. 

227. Modification of Wyatt.-"l')y reason of the tediousness of 
the method of Chatard given alK)ve, Wyatt has sought to shorten 
the process by the following modification.^* 

The ])resence of tluorin having been establishe(l by a qualita- 
tive test, its estimation is secured as follows : 
Phosphates of America, 4lh Edition, 1892 : 149, 



24 1>1 



MODIFICATION OF WYATT 



265 



' (• it 
■'I 



Five grams of the finely ground phosphate are fused in a 
platinum dish with 15 grams of the mixed carbonates of sodium 
and potassium and two grams of very fine sand. After fusing 
very thoroughly with a strong heat for a quarter of an hour, the 
dish is removed from the fire and cooled. Its contents, dis- 
solved in hot water, are then put into a lialf-liter flask, and a 
considerable excess of ammonium carbonate is added to the 
liquid. All the soluble silica falls otit of solution, and the flask, 
after cooling, is made up to the mark with distilled water, well 
shaken, and then set aside for 24 hours to settle. At the end 
of this time 200 cubic centimeters are carefully decanted through 
a filter; the filter is w^ell washed, and the filtrate, after being 
nearly neutralized with hydrochloric acid, is treated with an 
excess of calcium chlorid solution. 

The precipitate, consisting of phosphate, fluorid, and some 
calcium carbonate, is allowed to settle, and is then carefully 
washed with boiling water, first by decantation several times, 
and finally on the filter. After being properly dried in the gas- 
oven, calcined, and cooled, the residue is treated with acetic 
acid, placed upon the water-bath, and evaporated to complete 
dryness. 

The calcium acetate is now well washed out by several treat- 
ments with boiling water, and the residue is brought upon a 
filter, dried, calcined, and weighed. The weight represents the 
calcium phosphate and fluorid contained in two grams of the 
original sample; and if the calcium phosphate in the residue 
be determined according to the usual methods, the ditTerence will 
be calcium fluorid and may be thus estimated. 

For this purpose the mixed phosphate and fluorid is placed in 
a platinum dish and the fluorin expelled by treatment with sul- 
furic acid. The residue is taken up with alcohol, too cubic cen- 
timeters, the undissolved portion washed with an additional, too 
cubic centimeters of alcohol, and the phosphoric acid determined 
m the alcoholic solution by precipitation as ammonio-magnesium 
phosphate. 

BVam/)/^.— Assuming the calcined residue of calcium phos- 
phate and fluorid in two grams of the original sample to have 






•fi 



in 



1 *, 



'^1 



• .*\ 






li 



.*'! 



f .« 






I . 



266 



AGRICULTURAL ANALYSIS 



amounted to 1.6 gram and the calcium phosphate in this quan- 
tity to have been determined as 1.540 gram, the calcium fluond^is 
thus proved to be 0.060 gram, and, therefore, 2 :o.o6o: :ioo:x_3 
per cent, calcium fluorid, which, multiplied by 0.4897, gives 1.46 

per cent, of fluorin. 

The above method, while shorter, is not to be preferred to the 
former process when great accuracy is desired. All the solu- 
ble silica may not fall out of the solution as Wyatt says. Agam, 
the method of separating the phosphoric acid can not be regarded 
as strictly accurate. Finally, the fluorin is calculated from small 
differences in the weight of very heavy precipitates, and all the 
error of the process may be found affecting the numbers for 
fluorin. For commercial purposes, however, the method has the 
merit of comparative brevity. 

228. Method of Rose.— Clarke and Hillebrand recommend 
the Rose modification of the method just described, in which 
chromium and any residue of phosphoric acid are removed by 
silver nitrate.-'' The previous separation of silica and alumina by 
carbonate of ammonium is advised instead of nitrate or chlorid, to 
avoid loss of fluorin on evaporation. l>y whatever method the 
silica is thrown out, the alkaline carbonate must be converted 
into nitrate and not chlorid if chromium and phosphorus are 
present. The solution at the time the silver nitrate is added 
should contain enough of undecomposed alkaline carbonate to 
cause a copious precipitation of silver carbonate in order to take 
up the acid set free. After heating and filtering the excess of 
silver is to be removed by sodium or potassium chlorid, sodium 
carbonate added, and the fluorin precipitated by calcium chlorid 
in excess. No ammonium salts should be present in the solution 
when the calcium chlorid is added, for these tend to hold the 
fluorin in solution. The remaining part of the operation is con- 
ducted as above described. Attention is called to the fact that 
there is no verv satisfactory qualitative test for the presence of 
fluorin. The usual method of heating the powdered substance by 
the blowpipe, with sodium metaphosph.ate on platinum foil, is 
not alwavs reliable. 



" U. S. Geological Survey, Bulletin 148, 1S97 : 57. 



:rl. 



'II 



METHOD OF LASNE 



267 



229. Burk's Modification of Carnot's Method. — -Carnot's method 
is based on the digestion of a substance containing silica and a. 
fluorid with sulfuric acid and conducting the silicon tetrafluorid 
evolved into a solution of potassium fluorid.^^ The reactions 
which take place are expressed by the following formulas : 

1. CaF, + H.SO^ = 2HF + CaSO,. 

2. 4HF + SiO. = SiF, + 2H..O. 

3. SiF, + 2KF = K,SiF,, 

The potassium fluosilicate separates in part and is completely 
precipitated by 90 per cent, alcohol. After standing, the precipi- 
tate is collected on a filter, washed free of potassium fluorid by 90 
per cent, alcohol, and dried to constant weight. 

Two-thirds of the fluorin in the dried product is derived from 
the mineral under investigation. The number representing the 
weight of the precipitate multiplied by 0.345 11 gives the fluorin, 
and this multiplied by 2.0527 gives the weight of the calcium 
fluorid corresponding thereto. Burk describes the apparatus suited 
to the conduct of the work, and states the conditions under which 
it is accurate.-^ The chief sources of error are : 

1. Moisture in the air or tubes through which the silicon tetra- 
fluorid passes. 

2. Fumes of sulfuric acid carried over in the air current or 
otherwise. 

3. Insoluble addition products of potassium fluorid with the 
silica of the glass. 

The methods of avoiding these sources of error are set forth 
in detail in the paper cited above. 

230. Method of Lasne. — The difliculties which have been men- 
tioned led Lasne to modify the method of separating the hydro- 
fluosilicic acid in such a way as to render it practicable and 
€xact.^® 

The modification of Lasne consists essentially in removing the 
hydrofluosilicic acid evolved by the action of concentrated sul- 
furic acid on natural phosphate by a current of dry air conducted 

^^ Coniptes rendus, 1892, 114: 750, 1003. 
^"'Journal of the American Chemical Society, 1901, 23 : 825. 
'* Bulletin de la Soci^t<::^ chimi(iue de Paris, 1888, [2], 50 : 167. 
Annales de Chimie analyticjue, 1897, 2 : 161, 182. 



't . '' K 



■ ^ ■ 






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ii 



i 

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• Hi 









i#f.*'' 



268 



AGRICULTURAL ANALYSIS 



I 



II 



into a solution of caustic soda, where the fluorin is retained and 
ultimately estimated. It does not matter that the fluorin in this 
case is accompanied with other gases, and with vapor of water, 
since these imi)urities are absolutely w^ithout inconvenience in 
the subsequent proceedings. The phosphates can be treated with- 
out previous calcination or preparation in any form, and after 
mixing with sulfuric acid the temperature can be raised just to 



Dry a 




-^ jiMpirator 




FPF 



Fig. 12. I,asne's Apparatus. 



Ihe point of ebullition, which promotes very greatly the speed 
of the reaction and the perfect separation of the fluorin. The 
o])eration is conducted as follows : 

A deflnite (juaniity of the pliosphate or any other body what- 
ever containing fluorin, provided it be decomposable by sulfuric 
acid, is introduced into a dry flask in which have been previously 
I)laced about 50 cubic centimeters of strong sulfuric acid and 10 
grams of flnely ground sand. The quantity of the phosphate em- 
ployed should be such as to secure, if possible, an amount con- 
taining 0.1 gram of calcium fluorid. Tn phos]>hates which are 
very poor in fluorin it will be necessary to use from 10 to 20 
grams. One of the great advantages of this process lies in the fact 
that it permits the employment of these great quantities of 
materials without in any way interfering with the accuracy of 
the analysis. The flask and receiving bottles employed in the 



II 






METHOD OF LASNE 



269 






o])eration are illustrated by the accompanying Figure 12. The first 
receiving flask (B) contains two and one-half grams of caustic 
soda in 25 cubic centimeters, and the second (C) a half a gram 
in the same volume of water. The second flask is connected 
with the aspirator, by means of which the current of air is drawn 
through the whole apparatus. At the beginning of the operation 
the current of dry air is drawn through slowly and the flask (A) 
is moderately heated until its contents are brought to near the 
boiling point. During the heating the flask should be frequently 
shaken to secure the even distribution of the heat throughout 
the mass, and avoid danger of breakage. In this condition the 
evolution of the fluorin is terminated in about three hours. A 
blank experiment should show that the sulfuric acid and sand 
employed are free of fluorin. Sulfuric acid and sand entirely 
free from fluorin may be easily secured by heating one liter of 
the acid for two or three hours with 100 grams of finely ground 
sand, previously washed with hydrochloric acid. After cooling, 
the acid is decanted into a dry glass-stoppered flask, and the 
residual sand is washed and dried. These reagents are, when 
prepared in this way, both free from fluorin. When the fluorid 
of silica is entirely evolved from the mixture, which is easily 
determined by observing that the contents of the flask become 
hnipid, the lamp is extinguished and the mass is allowed to cool 
until the flask can be easily handled. It is then removed and the 
delivery tube washed into a dish into which subsequently are 
poured the contents of the two receiving flasks, and their con- 
necting tubes are washed with water. The solution obtained in 
this way should still be freely alkaline, as indicated by forming 
a red color with phenolphthalein. If it be not alkaline, a suffi- 
cient quantity of caustic soda should be added. The contents of 
the dish are heated for half an hour to 100° for the purpose of 
decomposing into hydrofluoric acid and silica the fluosilicate 
which has been formed at first. The total volume of the solution, 
in order to facilitate the operation, should be reduced by evap- 
oration to about TOO cubic centimeters. After partial cooling the 
solution is saturated with carbon dioxid, the flask being covered 
meanwhile to prevent any loss by the projection of the liquor 
with the escaping gas. The residual liquor and the wash water 



. il 

\ '■ nl 



% 
I 






270 



AGRICULTUR^KL ANALYSIS 



I 



< 



coming from the covered dish are introduced into a flask grad- 
uated to 125 cubic centimeters, which should not be completely 
filled. Some solid carbonate of ammonia is added and the mix- 
ture heated for half an hour to about 50°, adding from time to 
time a little of the carbonate. By this process the silica is, as a 
rule, completely precipitated. Nevertheless, as it is important 
that not the least trace of silica be in solution, it is recommended 
to finish the separation with oxid of zinc. For this purpose the 
volume of the mixture is completed to the mark and the contents 
of the flask filtered into a dried beaker. One hundred cubic cen- 
timeters of the filtrate are placed in a porcelain dish and 10 cubic 
centimeters of solution of oxid of zinc in ammonia, in all about 
0.3 gram of oxid of zinc, are added. The solution is evaporated 
almost to dryness and some water added, and the evaporation 
repeated in this way two or three times. The preci])itate of car- 
bonate of zinc formed carries down the last traces of silica. The 
whole precipitate is finally collected upon a filter and washed. 
Since the (juantity of carlx)nate of soda present is not exactly 
known, there are added to the solution a few drops of tropeolin, 
and carefully, afterwards, diluted hydrochloric acid, until a rose 
tint is produced, and without waiting to cubic centimeters of a 
solution of carbonate of soda containing 300 grams of the crys- 
tallized salt i^or liter. This quantity of carbonate of soda should 
])e prepared in advance, so that it can be added instantly, as it is 
not safe to leave the solution acid, because it will attack the glass 
and bring a small (juantity of silica into solution. After the addi- 
tion of the carbonate of soda solution the mixture is boiled for 15 
minutes. To the nearly boiling solution there is added a slight 
excess of calcium chlorid, say about 10 cubic centimeters of a 
solution containing 300 grams of the crystallized calcium chlorid 
l>er liter. Stir thoroughly and allow to settle for a short time 
and filter while still hot. Wash the precipitate, which is com- 
posed of calcium carbonate and calcium fluorid. The precipitate 
is dried and burned, the temperature being raised with great cau- 
tion, so as to avoid a partial fusion, a phenomenon which is pro- 
bably due to the existence of a fluocarbonate which has not yet 
been isolated. The ignition is conducted in a large platinum cruci- 



CARNOT S MODIFICATION 



271 



ble. The capsule, after cooling, is covered with a funnel, and from 
30 to 40 cubic centimeters of water are poured upon the ignited 
precipitate, followed by three cubic centimeters of glacial acetic 
acid. After the evolution of carbon dioxid is finished the funnel 
is removed and washed, the residual liquor is evaporated to 
near dryness, water added, and the evaporation repeated two 
or three times and finished by evaporating to dryness. The res- 
idue is taken up with 30 or 40 cubic centimeters of water con- 
taining one per cent, of acetic acid. After heating for a mo- 
ment the fluorid of calcium which remains insoluble is collected 
and washed with water slightly acidulated with acetic. The 
washing is finished with pure water. The absence of sulfates in 
the last wash water should be ascertained by a careful test. It 
is rather difficult to filter the calcium fluorid, and some precau- 
tions to avoid a turbid filtrate w ill be found necessary. The pre- 
cipitate is dried, ignited and the fluorid of calcium, obtained in a 
perfectly pure state, weighed. The purity of the residue can be 
determined by dissolving with concentrated sulfuric acid, after- 
wards diluting a little and precipitating by alcohol. The sulfate 
of lime obtained in this way should correspond, molecularly, to 
the original calcium fluorid. According to Lasne, this method, 
if carefully followed, gives results which are rigorously exact. 

231. Carnot's Modification. — Carnot has proposed to shorten 
the method of Lasne in the following manner: 

In place of receiving the fluorid of silicium in caustic soda, 
the gas is conducted into a solution of fluorid of potash, the 
delivery tube being plunged into mercury to avoid obstruction. 
There is thus formed a fluosilicate, which is precipitated by 
alcohol, collected upon a tared filter and weighed. Lasne con- 
sidered this method to be, in fact, more rapid, but dangerous. It 
is always inconvenient, according to him, to use in determination 
a body of the same nature as that which is to be determined, a 
process which renders all final verification impossible. 

Goutal has criticised the method of Lasne, preferring the shorter ■ 
method of Carnot mentioned above.^^ His objections to the 
method of Lasne are based ujx^n the following: 

^ Annales de Chitnie analytique, 1897, 2 : 401. 



■ f 'I 



m 



1 n Si 



I ti 






f 



')i 









f M 






272 



AGRICULTURAL ANALYSIS 



Hi 



(i) Five or six reagents are required. ' 

(2) Evaporations and ebullitions of alkaline liquids are carried 
on in glass vessels, which are subject to attack. 

(3) The precipitate weighs only a few centigrams. 

(4) The precipitate is mixed with silica. 

(5) The ])recipitate is soluble in the successive reagents em- 
ployed. 

'I'hese objections are answered by Lasne.^^ 

Lasne admits that if the phosphates in which tluorin is to be 
determined are previously ignited, many of the objections to the 
shorter method proposed by Carnot are removed, but he fears 
that there is danger of loss of fluorin, as well as of water, by 
calcination, and adds that the calcination of phosphates, and more 
particularly of bones, is an operation which is neither easy nor 
rapid, if it be desired to burn away the last traces of carbon. 

232. Protection of Glassware in Working with Fluorin. — Carnot 
has pr(jposed to coat ilu surfaces of tiasks and tubes used in the 
determination of fluorin with gum-lac.^^ 

According to Carnot, this lacquer protects completely the glass 
from the action of the solution of hydrofluoric acid. 

233. Fluorin in Bones. — According to Carnot, the deposits of 
phosphates have been formed in the following manner: 

( 1 ) The accumulation of phosphatic animal debris, etc., along 
the banks of the ocean or in lakes or lagoons. 

(2) The impregnation of these phosphates in the fluorid of cal- 
cium contained in the sea waters. Carnot has demonstrated the 
presence and determined the proportion of fluorin in the waters 
of the ocean, and has shown in the laboratory, by synthetic ex- 
])eriments, the gradual fixation of fluorin in bony deposits. 

The fluorin which is a constituent of mineral phos- 
phates is probably derived from bones. According to the 
researches of Carnot, there is often a considerable quantity 
of calcium fluorid in bones and teeth. ^*- In fossil bones very large 
quantities have been found, reaching as high as 6.21 per cent, of 

•*" Annales de Chiinie analytique, 1898, 3:6. 
^^ Annales (les Mines, 1893, [9], 3 : 138. 
" Coniptes rendus, 1S92, 114 : 1189. 

Annales de Cbimie et de Physique, 1855, 1 : 47. 



?; 



lODIN IN PHOSPHATES 



273 



calcium fluorid in a fossil bone in a phosphate from the Charles- 
ton deposits. Gabriel has suggested a means of determining 
a minimum limit of fluorin in bones and teeth by the develop- 
ment of etchings in com])arison with known quantities of pure 
calcium fluorid. The minimum quantity of calcium fluorid neces- 
sary to produce a distinct etching, in known conditions, having 
been determined, the test is applied to known weights of ignited 
bone or teeth. He concludes from his results that the ash of 
bones and teeth often contains less than one-tenth per cent, of 
fluorin. Since, however, there is a loss of fluorin from calcium 
fluorid on ignition, the whole of the fluorin may not have been 
available in tlie tests described. 

234. lodin in Phosphates. — The presence of iodin has been de- 
tected in many natural ])hosi)hates and is of interest in the dis- 
cussion of the problem of their origin.*"^ A sample of phosphate 
from Florida was found to contain 0.014 per cent, of iodin. This 
element has also been observed in the phosphates from other lo- 
calities, as has been shown by Gilbert. A qualitative test for 
the detection of iodin may be applied in the following manner: 
Some finely ground phosphate is mixed with strong sulfuric acid 
and the gases arising from the reaction are aspired into some 
carbon disulfid or chloroform. The violet coloration arising 
indicates the presence of iodin. The gases carrying the iodin 
may also be brought into contact with starch-paste producing 
the woll known l)lue color. 

The quantity of iodin present in a phos])hate is rarely more 
than one or two-tenths of one per cent. It can be determined as 
a sflver salt, in the absence of chlorin or by any of the standard 
methods found in wnrk'^ on quantitative analysis. 
^ Iodin is quite a constant constituent of Florida phosphates. 
I^or a quantitative determination, the sample is treated with an 
excess of strong sulfuric acid in a closed flask and during the 
decomposition a stream of air is aspired throui^li the flask and 
caused to l)u])l)le through absorption bulbs containing sodium or 
potassium hydroxid in solution. 

The temperature of the decomposition may be raised to about 
200°. After the distillation is complete the sodium iodid formed 
"I.'KnKrais, 1895, 10 165. 



in 



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' 41 



i -sj 



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274 



AGRICULTURAL ANALYSIS 



i5 titrated by treating with potassium permanganate.^* The reac- 
tion is represented by the equation : NaI+2KMn04+H20= 
Nal03+2KOH+2Mn02. The iodin also may be set free and 
determined in the usual wav bv titration with standard sodium 

thiosulfate solution. 

The titration of free iodin is represented by the following re- 
action : 

2NaoSA+2l=2XaI-fNa.S40e. 

In tliis reaction thiosulfuric acid is converted into tetrathionic 
acid and the free iodin into hydriodic acid, both of which com- 
bine with the sodium present. The decinormal solution of sodium 
thiosulfate may be used. Grind the crystals of the salt to a fine 
ixnvder, dry between blotting papers, and use 24.8 grams of the 
dried salt per liter. The (juantity of iodin found in phosphates 
is so minute that it is hardly worth while to make a quantitative 
determination of it. 

235. Occurrence of Chromium in Phosphates. — In some phos- 
phates a small quantity of chromium has been found. In a 
sample of phosphate from the Island of Los Roques in the Car- 
ibbean Sea, Gilbert found three-fourths per cent, of chromium 
oxid (Cr^.O;;). The phosphates containing chromium have a 
greenish color and are characterized by great insolubility in solu- 
tions containing organic acids. The chromium is to be deter- 
mined by the usual methods described in mineral analysis. 

236. Estimation of Vanadium. — In the complete analysis of 
basic slags it becomes necessary to determine the presence of 
vanadic mixture with this solution until a drop of the clear liquor. 
the volumetric process of Lindemann.*'*'^ It is conducted as fol- 
lows : Dissolve four grams of the finely powdered slag in 60 cub- 
ic centimeters of dilute sulfuric acid (i 14), boil for a few min- 
utes, cool, make the volume up to 100 cubic centimeters, filter and 
add decinormal potassium permanganate solution in slight excess 
to an aliquot ])art of the filtrate to secure the oxidation of the vana- 
dium to vanadium pentoxid. Add, drop by drop, a weak solution 
of ferrous sulfate until the pink color just disappears. Prepare 

'* Suttcm, Volutnetric Analysis, 9th Kdition. 1904 : 219. 
] '* Ueber die quantitative liestimninng des Vanadins in Eisenerzen, 1878. 
Zeitschrift fiiranalytische Cheniie, 1879, 18 : 99. 






ESTIMATION OF VANADIUM 



275 



a ferrous sulfate solution by dissolving 2.183 grams of piano wire 
in sulfuric acid and making the volume to one liter. Titrate the 
vanadic rriixture with this solution until a drop of the clear liquor, 
removed and brotight in contact with potassium fcrricyanid, shows 
a distinctive blue-green color. 

One cubic centimeter of the ferrous sulfate solution is equiva- 
lent to 0.002 gram of vanadium, 0.002888 gram of vanadium di- 
oxid, and 0.003648 gram of vanadium pentoxid. The ferrous 
sulfate solution may also be made and standardized by any of the 
approved methods in common use. 

The method described by Blair, designed especially for the es- 
timation of vanadium in iron and steel, is conducted in the follow- 
ing manner :^« Five grams of the drillings are dissolved in 50 
cubic centimeters of nitric acid of 1.24 specific gravity. The solu- 
tion is evaporated to dryness in a porcelain dish and heated there- 
after until the nitrates are nearly decomposed. After cooling, 
the dried mass is transferred to a mortar and finely ground 
with 30 grams of dry sodium carbonate and three grams of 
sodium nitrate. The finely ground materials are placed in a 
platinum dish and fused for an hour at a high temperature. 
vSpread the fused mass over the sides of the dish while cooling, 
and afterwards dissolve in hot water, filter, and wash until the 
volume is a little over half a liter. Add nitric acid to decompose 
carbonates, but not completely, and boil to get rid of carbon 
dioxid, being careful to keep the mass always slightly alkaline. 
Add nitric acid, drop by drop, until slightly in excess, and then 
sodium carbonate to marked alkalinity, boil, and filter. Add a 
slight excess of nitric acid to the filtrate, and the development of 
a yellow color will indicate the presence of vanadic acid. Add 
to the sohttion a small quantity of mercurous nitrate and then an 
excess of mercuric oxid, suspended in w^ater to render the solu- 
tion neutral and insure the complete precipitation of mercurous 
vanadate. The mercurous salt also precipitates phosphoric, 
chromic, ttingstic, and molybdic acids which may be present. 
I>oil, fihcr, and wash the precipitate with hot water, dry, and 
Ignite. Fuse the residue with sodiutn carbonate and a little 
nitrate. Dissolve the fused mass, after cooling, in a little water 

** The Chemical Analysis of Iron, 6th Edition, 1906 : 203. 



1? 



I 



i I 



I 



fi 






m 






: I 

■ III 






n 









\m ■ : 



276 



AGRICU1.TURAL ANALYSIS 



and filter. Add to the filtrate amnioniuni chlorid in excess 
about 3.5 grams for each 10 cubic centimeters of the solution, 
and allow to stand, with occasional stirring, for some time. Am- 
monium vanadate, insoluble in a saturated solution of ammonium 
chlorid, separates as a white powder. It is necessary to keep the 
solution alkaline, and a drop of ammonia should be added from 
time to time for this ])urpose. The ap])caranco of a yellowish 
tint at any time indicates that the solution has become acid, and 
this acidity must be corrected, or else tiie results will be too low. 
Separate the ammonium vanadate by filtration ; wash first with 
a saturated solution of ammonium chlorid containing a little free 
ammonia, and then with alcohol. Dry, ignite, and moisten with a 
few drops of nitric acid ; again ignite to obtain the compound as 
vanadium pentoxid, V^O.. This compound contains 56.22 per 
cent, of vanadium. 

The method of Rosenheim and llolverscheit may also be used.*^^ 
Tt is based on the preliminary precipitation of the vanadic acid as 
a bariinn or lead salt. The substance supposed to contain vana- 
dium is first brought into solution in such a manner as to secure 
it as vanadic acid, which is then precipitated with barium chlorid 
or lead acetate. The precipitate is boiled with hydrochloric acid 
and i)otassium bromid, and the liberated bromin determined bv the 
quantity of iodin set free from potassium iodid. in the absence of 
bodies, such as molybdic acid, which are reduced by sulfurous 
acid or hydrogen sulfid the vanadic acid may also be determined 
by reducing it with one of these reagents and, after removing the 
excess by boiling, titrating the vanadium tetroxid with potas- 
sium permanganate. When vanadic and ])hosphoric acids occur 
together the former may be first reduced to tetroxid with sulfurous 
acid, and after expelling excess of this reagent, the phosphoric 
acid may be separated with molybdate solution and removed by 
filtration When the amount of vanadic acid is large the phos- 
phoric acid should be separated ra])idly at 55°-6o°, using a con- 
siderable excess of the molybdate ; or the vanadic acid may first be 
determined in the solution volumetrically by the bromin pro- 
'^ Ueher Vanadinwolfranisame, Dissertation, Berlin, 1888. 

Ueber die quantitative Bestininiung des Vanadins. Di.ssertation, Ber- 
lin, 1890. 



MANUFACTURE OF SUPERPHOSPHATES 



2-]-] 



cess above described, and afterwards the phosphoric acid 
obtained by evaporating to dryness with a little sulfuric acid, 
taking the residue up with water, reducing the vanadic w^ith sul- 
furous acid and precipitating the phosphoric acid with molyb- 
date solution as described above. 

CHEMISTRY OF SUPERPHOSPHATE MANUFACTURE 

237. Chemical Changes in the Manufacture of Superphosphates. 
— In this country the expressions "acid" and "super" as applied 
to phosphates are used interchangeably. A more correct use of the 
terms would designate by "acid" the phosphate formed directly 
from tricalcium phosphate by the action of sulfuric acid, while by 
"super" would be indicated a similar product formed by the action 
of free phosphoric acid on the same materials. In Germany the lat- 
ter compound is called 'Vlouble phosphate." 

The reaction which takes place in the first instance is repre- 
sented by the following formula : 

3Ca3 ( PO, ) 2+6H2SO,+ 1 2H,0=4H3PO,-f-Ca, ( PO, ) .-}- 
6(CaSO,.2lLO) ; 

and 4H,PO,H-Ca3(POJ2+3H20=3[CaH,(POj2-H,0]. 

A simpler form of the reaction is expressed as follow^s : 

Ca., ( PO, ) o-[-2HoSO,H- sH.O 
=CaH,(P0,),.H,0-f2[CaS0,.2H,0]. 

If 310 parts, by weight, of finely ground tricalcium phosphate 
be mixed with 196 parts of sulfuric acid and 90 parts of water, 
.'ind the resulting jelly be quickly diluted with a large quantity 
of water, and filtered, there will be found in the filtrate about 
three-quarters of the total phosphoric as free acid. If, however, 
the jelly, at first, formed as above, be left to become dry and hard, 
the filtrate, when the mass is beaten up with water and filtered, 
will contain monocalcium phosphate, Q2\\^{VO^)^. 

If the quantity of sulfuric acid used be not sufficient for com- 
plete decomposition, the dicalcium salt is formed directlv accord- 
ing to the following reaction : 

Ca3(PO,),+H,SO,+6H,0 
=CXH, ( PO J 2.4H,0+CaSO,.2H,0. 
This arises, doubtless, by the formation, at first, of the regular 






^'1 



1 



im 



i 






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78 



AGRICULTURAL ANALYSIS 



inonocalciuni salt and the further reaction of this with the tri- 
-calcium compound, as follows : 

CaH,(PO,),+H,0+Ca3(POJ,+7H,0 . 
=:2[Ca,H.(PO,)24H20]. 

This reaction represents, theoretically, the so-called reversion 
•of the phosphoric acid. When there is an excess of sulfuric acid 
there is a complete decomposition of the calcium salts with the 
production of free phosphoric acid and gypsum. The reaction 
is represented by the following formula: 

Ca3 ( PO4 ) 2-f •sH.vSO.+GH^O 

:::=2H3PO,+3[CaSO,.2H20]. 

The crystallized gypsum absorbs the six molecules of water in 
its molecular structure. While the above reactions represent the 
theoretical conditions, there is a wide divergence from them in 
actual manufacture. In the case of dissolved bone, especially, the 
actual quantity of sulfuric acid used is not so great as is indi- 
cated. The proportions of acid and raw materials are necessarily 
changed from time to time to meet the emergencies which may 
arise. 

238. Reactions with Fluorids.— Since calcium fluorid is pres- 
ent in nearly all mineral phosphates, the reactions of this 
compound must be taken into consideration in a chemical study 
of the manufacture of acid phosphates. When treated with sul- 
furic acid the first reaction which takes place consists in the for- 
mation of hydrofluoric acid : CaFo -f HoSO, = 2HF -f CaSO,. 
Since, however, there is generally some silica in reach of the 
nascent acid, all, or a portion of it, combines at once with this 
f^ilica, forming silicon tetrafluorid : 4HF+SiO,=2H20+SiF,. 
This compound, however, is decomposed at once in the presence 
of water, forming hydrofluosilicic acid: 3SiF,-f 2H20i=SiOo+ 
2H2SiFrt. \The presence of calcium fluorid in natural phosphates 
is extremely objectionable from a technical point of view, both 
on account of the increased consumption of oil of vitriol which 
It causes, and also by reason of the injurious nature of the gaseous 
fluorin comi)ounds produced) Each 100 pounds of calciimi flu- 
orid entails the consumption of 125.6 pounds of sulfuric acid, for 
which no economic return is secured. 






IRON AND ALUMINA COMPOUNDS 



27.) 



I ! 



239. Reaction with Carbonates. — Most mineral phosphates con- 
tain calcium carbonate in varying quantities. This com- 
pound is decomposed on treatment with sulfuric acid according 
to the reaction: CaCOs-f H^SO.^CaSO.-f H^O-f CO^. When 
present in moderate amounts, calcium carbonate is not an objec- 
tionable impurity in natural phosphates intended for acid phos- 
phate manufacture. The reaction with sulfuric acid which takes 
place produces a proper rise in temperature throughout the mass, 
while the escaping carbon dioxid i)ermeates and lightens the whole 
mass, assisting thus in completing the chemical reaction by leaving 
the residual mass porous, and capable of being easily dried and pul- 
verized. Where large quantities of carbonate in proportion to 
the phosphate are present the sulfuric acid used should be dilute 
enough to furnish the necessary water of crystallization to the 
gypsum formed. For each 100 parts, by weight, of calcium car- 
bonate, 80 parts of sulfuric anhydrid are necessary, or 125 
parts of acid of 1.7 10 specific gravity=6o° Beaume. 

In some guanos a part of the calciutn is found as pyrophos- 
phate, and this is acted upon by the sulfuric acid in the follow- 
ing way : CaoPA+H,SO,r:=:CaHoP A+CaSO,. 

240. Solution of the Iron and Alumina Compounds. — Iron may 
occur in natural phosphates in many forms. It probably is 
most frequently met with as ferric or ferrous phosphate, seldom as 
ferric oxid, and often as pyrite, FeSo. The iron also may sometimes 
exist as a silicate. The alumina is found chiefly in combination 
with phosphoric acid, and as silicate. 

\Miere a little less sulfuric acid is employed, as is generally 
the case, than is necessary for complete solution, the iron phos- 
phate is attacked as represented below : 

3FePO,-f3H,SO,=FePO,.2H3PO,-fFe,(SO,)3. 

When an excess of sulfuric acid is employed, the formula is 
reduced to the simple one : 

2FePO,+3H,SO,=2H3PO,+Fe2(SO,),. 

A part of the iron sulfate formed reacts with the acid calcium 
phosphate present to produce a permanent jelly-like compound, 
difficult to dry and handle. As much as two per cent, of iron 



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280 



AGRICULTURAI, ANALYSIS 



SOLUTION OF A MINERAL PHOSPHATE 



28 r 



'^1 






phosphate, however, may be present without serious interference 
with the commercial haiidhnjj^ of the product. Ry usin.^ more 
sulfuric acid, as much as four or five per cent, of the iron phos- 
phate can be held in solution. Larger quantities are very trouble- 
some from a commercial i)oint of view. The reaction of the 
ferric sulfate with monocalcium phosphate is as follows: 

3CaH(POj,+FeJSOj3.+4H,0=2(FePO,.2H3PO,.2H.O) + 
3CaSO, 

Pyrite and the silicates containing iron are not attacked by 
sulfuric acid and these compounds are therefore left, in the final 
product, in a harmless state. If the pyritic iron is to be brought 
into solution ac|ua regia should be employed. 

\\ ith sufficient acid the aluminum phosphate is decomposed 
with the formation of aluminum sulfate and free phosphoric acid: 

AlPO,-f3H,SO,zrrAl,(SOj3-f2H3PO,. 

241. Reaction with Magnesium Compounds.— The mineial phos- 
phates, as a rule, contain but little magnesia. When pres- 
ent it is probably as an acid salt, MgHPO,. Its decomposition 
takes place in slight deficiency or excess of sulfuric acid, respect- 
ively, as follows : 

2MglT I >0, + H,S0,+2H,0= [ MgH, ( PO, ) ...2H.O] + MgSO, 
and MgHPO, + H,SO,=:H3PO,-f MgSO,. 

The magnesia, when in the form of oxid, is capable of pro- 
ducing a reversion of the monocalcium phosphate, as is shown 
below : 

CaPT,(POJ,.+MgO^CaMgIL(POJ^.+HA 
One part by weight o"f magnesia can render three and one-half 
parts of soluble monocalcium phosphate insoluble. 

242. Determination of Quantity of Sulfuric Acid Necessary for 
Solution of a Mineral Phosphate.— The theoretical quantitv of 
sulfuric acid required for the proper treatment of anv phosphate 
may be calculated from its chemical analvsis and by the formulas 
and reactions already given, lor the experimental determination 
the method of Rumplor mav be followed.-^'* 

Twenty grams of the fine phosphate are placed in a liter flask 
" Kaufliche DUngestolTe und ihre Ai.win<liniK, Ith Kdilion, 1897 : 81. 



with a greater quantity of accurately measured sulfuric acid than 
is necessary for complete solution. The acid should have a 
specific gravity of 1.455 o^ 45° ^- "^^^^ mixture is allowed to 
stand for two hours at 50°. It is then cooled, the flask filled 
with water to the mark, well shaken, and the contents filtered. 
Fifty cubic centimeters of the filtrate are treated with tenth-nor- 
mal soda-lye, free of carbonate, until basic phosphate begins to 
separate and becomes permanent after shaking. The excess of 
acid is then calculated. Example : Twenty grams of phosphate 
containing 28.3 per cent, of phosphoric acid, lO.O per cent, of 
calcium carbonate, 5.5 per cent, of calcium fluorid, and 2.4 ix-r 
cent, of calcium chlorid were treated as alx)ve with 16 cubic centi- 
meters of sulfuric acid containing 10.24 grams of sulfur trioxid. 
In titrating 50 cubic centimeters of the fiUrate obtained as de- 
scril)ed above, 10.4 cubic centimeters of tenth-normal soda-lye 
were used, ecpiivalent to 0.0416 gram of sulfur trioxid. Then 10.24 
X50-M000— o.5i20=total sulfur trioxid in 50 cubic centimeters 
of the filtrate, and 0.5120 — 0.0416--0.4704 gram, the amount of 
sulfur trioxid consumed in the decom])osition. 

Therefore the sulfur trioxid required for decomposition is 
47.04 per cent, of the weight of the phosphate emj)loyed. 
One hundred parts of the phosphate would, therefore, require 
47.04 parts of sulfur trioxid e(iual to 73.6 parts of sulfuric acid of 
1.710 specific gravity or 92.1 parts of 1.530 specific gravity. 

A more convenient method than the one mentioned above, con - 
sists in treating a small cpiantity of the phosphate, from one-half 
to one kilogram, in the laboratory, or 50. kilograms in a lead 
lx)x just as would be practiced on a large scale. A few tests 
with these small quantities, followed by drying and grinding, 
will reveal to the skilled operator the approximate quantity and 
strength of Mil f uric acid to l)e used in each case. The quanti- 
ties of sulfuric acid as determined by calculation from analyses 
and by actual laboratory tests agree fairly well in most instances. 
There is, however, sometimes a marked disagreement. The 
general rule of practice is to use always an amount of sulfuric 
acid sufficient to produce and maintain water-soluble phosphoric 
acid in the fertilizer, but the sulfuric acid must not be used in 



^4 






282 



AGRICULTURAL ANALYSIS 



it £ 



At 50° B. 


At 52° B. 


At 54° B. 


At 55^' H 


1-5^7 


1.446 


r.382 


1.352 


1.558 


1.485 


1.420 


r.390 


I -930 


1.839 


1.756 


1. 721 


1.565 


1.495 


1.428 


1. 411 


2.010 


1. 916 


1.830 


1.794 


1.860 


1-775 


1.690 


1.660 



such quantity as to interfere with the subsequent drying, grind- 
ing, and marketing of tlie acid phosphate. 

For convenience, tlie following table may be used for calcula- 
ting the quantity of oil of vitriol needed for the entire decomposi- 
tion of each unit of weight of material noted. 

Onk Part hv Wright of Each Substancr Below Requires : 

Sulfuric Acid by Same Unit of Weight. 

At 48° B. 

Tricalciuni phosphnte ^59^ 

Iron phosphate f 630 

Ahiniiniiin phosphate 2.025 

Calcium carbonate 1.640 

CalciuTii fliiorid 2.006 

Magnesium carbonate i .940 

Example. — Suppose for example a phosphate of the following 
composition is to be treated with sulfuric, acid ; viz.,'^" 

Moisture and organic matter 4.00 per cent."*'' , 

Calcium phosphate 55.00 " 

Calcium carbonate 3.00 

Iron and aluminum phosphate nearly all alumina 6.50 

Magnesium carbonate 0.75 

Calcium fluorid 2.25. ** 

Insoluble 28.00 

Using sulfuric acid of 50° P>., the following quantities will be 
required for the weights mentioned: 

Kilos of acid required. 
Calcium phosphate, fifty-five kilos 8^.44 

" carbonate, three and a half kilos 5.48 

" fluorid, two and a quarter " 4^2 

Aluminum and iron i)hospliate, six and a half kilos 12.55 

Magnesium carbonate, three-quarters of a kilo 1.40 



< t 



( ( 



Total 68 kilos 



107.39 



Since only a partial decomposition is attained in actual manu- 
facture the quantity of 50° Beaume acid required is oiten less than 
the weight of phosphate treated. . ^^, f 

243. Phosphoric Acid Superphosphates.— If a mineral phosphate 
be decomposed by free phosphoric acid in place of sulfuric acid, 
the resulting compound will contain about three times as much 
^* Wyatt, Phosphates of America, 4th Edition, 1892 ; 128. 



1 i 



PHOSPHORIC ACID IN BASIC SOILS 



283 



"rl 



in 



available phosphoric acid as is found in the ordinary acid phos- 
phate. The reaction takes place according to the following 
formulas : 

(1) Ca3(POJ,+4H3PO,+3H,0=3[CaH,(PO,),.H,0]. 

(2) Ca3(POj2+2H3PO,+ i2HoO=3[Ca;H2(POJo.4H,0]. 

In each case the water in the final product is probably united as 
crystal w^ater w^ith the calcium salts produced. The monocal- 
cium salt formed in the first reaction is soluble in water, and the 
dicalcium salt in the second reaction, in ammonium citrate. 
Where fertilizers are to be transported to great distances, there 
IS a considerable saving of freight by the use of such a high- 
grade phosphate, which may, at times, contain over 40 per cent, 
of available acid. The phosphoric acid used in this process is 
made directly from the mineral phosphate by treating it with an 
excess of sulfuric acid. 

244. Fixation of Phosphoric Acid in Basic Soils. — The problem 
of holding phosphoric acid in the soil probably does not come 
within the scope of this manual, except as incident to the character 
and time of its application. This subject has been studied by 
Crawley.*^ 

■ Experimentally, the determination of the holding powers of 
the soil for the phosphoric acid obtained, depends upon the same 
methods as are descril)ed for the absorption of salts by soils. *^ 
In the irrigated soil with which Crawley worked, it was 
found that, when the application of fertilizer containing water- 
soluble phosphoric acid was followed immediately by irrigation, 
more than one-half of the soluble phosphoric acid remained in 
the first inch of the soil and more than nine-tenths in the first three 
inches, and practically the whole of it within the first six inches, 
of the surface. Crawley concludes from the results of his investi- 
gations that the water-soluble phosphoric acid does not become 
so widely distributed, in the case of heavy rains or irrigation 
beneath the siiiiface, as has been expected. In this connection 
however, atteWt'Jon should be called to the fact that the Hawaiian 

*^' Journal of the American Chemical Society, 1902, 24 : 11 14. 

'' Principles and Pr^^tjce of Agricultural Analysis, 2nd Edition, 1906, 



M3, 



and I'rari^ce ot Agri 

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284 



AGRICULTURAL ANALYSIS 



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"i i 



soils on which Crawley worked, are very strongly basic and hence 
are in a condition better suited to fix and bold the phosphoric 
acid than the acidic soils with which the chemist is usually called 
upon to work. The obvious conclusion from an experimental 
work of this kind is that in determining the power of any par- 
ticular soil for holding the phosphoric acid applied to it, its 
character, especially as regards its acidity or basicity, should be 
carefully considered. 

245. Absorption of Phosphoric Acid of Superphosphates."-'— Mr. 
Jofifre states that contrary to what is usually thought, the com- 
binations .soluble in water appear to be absorbed bv vege- 
tation. The proportion absorbed is, without doubt, very small, 
but it may have a very great importance because the absorption 
takes place at a moment when the plants have used up the ma- 
terial in the seed and have not yet developed sufficiently to evapo- 
rate the large quantity of water and to be able thus to extract from 

the soil the u.seful substances, difficultly soluble, which there 
fxist. 

This theory explains perfectly the results of the remarkable 
researches of Schloesing and Prunet who have found that, when 
tertihzers are planted in the rows, thev produce greater effects 
than whe>i they are mixed with the soil. This evidence depends 
upon the fact that when they are planted in rows, thev become 
soluble less rapidly and the plants thus have more time '»o absorb 
the combmations of phosphoric acid soluble in water. 

On page 698 of the same volume, Joffre continues the dis- 
cu.ss.on of the subject. In this communication he has subjected 
to field experiments, the operations which he has previously con- 
ducted in the laboratory. He says: "Moreover, in the culture 
experiment made in pure sand where there was nothing which 
could produce insolubility of phosphate .soluble in water and 
where it is seen that this body causes an increase iir'tii'e crops, it is 
necessary to admit that the combinations of phosphoric acid solu- 
ble in water enter into the plant and are assiimlaf.-d there I 
have not said that insoluble phosphate is without'ntilitv in agricul- 
ture. It produces, indeed, in certain earth effects which are as 

" Bulletin de la Society chimique de Park'AS'g?, [3], 13 .. 522 



i¥ 



« % • 






PHYSICAI, CONDITION 01* AVAILABILITY 



285 



m 



beneficial as the soluble phosphate, Imt in the greater part of soils, 
if it produces an action, this action is less than that of superphos- 
phates and the inferiority of this action appears to be caused, at 
least in part, because no portion of it can enter immediately into 
the plant in a condition of aqueous solution. 

"To resume, the whole of my experiment seems to make clear 
that the favorable action of superphosphate is not only caused by a 
greater dissemination of the combinations of phosphoric acid in 
the arable earth, but that it is also necessary to take into account 
the absorption in the form of combinations, soluble in water, of a 
portion of soluble phosphoric acid of superphosphates. If we 
desire to obtain a maximum result it is necessary to distinguish two 
sorts of soil ; first, the soil analogous to those, of which numerous 
•examples are found in Bretagne, in which insoluble j^hosphates 
succeed as well as superphosphates and where it is natural to em- 
j)loy phosphate simply ground. Second, the other soils which are 
far more numerous and in wliich the phosphoric acid fertilizers in 
combinations soluble in water are absolutely indispensable to ob- 
tain the maximum effect." 

246. Physical Condition of Availability. — In general it may 
be said that the physical state of subdivision of raw phosphates 
and basic slags is one of the most important factors in respect 
•of their availability. This degree of fineness, however, depends 
for its efficiency largely on other conditions, especially where arti- 
ficial means are employed for determining availability. For 
this reason it is advisable, when determining the availability of 
these materials by chemical means, to employ extremely dilute 
solutions. The method of Dyer depends on the use of an orgruiic 
acid and of Moore upon the use of a mineral acid ; both require 
great degrees of attenuation. *'' Only by the use of some such re- 
agent can the conditions which occur in nature be simulated, 
yet it must not be considered that the same degree of attenuation 
must be present in the artificial means as in the natural. Otherwise 
the time of experimental determinations of tlv.^ artificial means 
would have to continue over several months instead of several 
hours. It is possible that a revision of the common idea respect- 

*' Principles and Practice of Agricultural Analysis, 2n(l Edition, 1906, 
1 =394, 459- 



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286 



AGRICULTURAL ANALYSIS 



ing the action which takes place in the soil will show that the 
plant itsrlf exudes no solvent material as has been assumed by 
many investigators, unless it be the excretion of carbon dioxid. 
The processes of solution which take place in the soil, from a 
study of all the conditions which obtain, must be regarded more 
as operations depending upon the soil itself than as largely in- 
fluenced by the growing plant. At the present time, however, 
the solution of the problem, experimentally, in so far as fineness 
of subdivision is concerned, has perhaps been well answered and 
it is now clearly understood that in so far as the assimilation 
processes go on in the soil, they are favored more particularly by 
the fineness of the subdivisions than by any other factor. Even 
in soils which are not distinctly acid the fineness of subdivision 
greatly favors solution, and in regard to the other causes of solu- 
tion and absorption of these bodies, excluding those due to 
weathering, it is probable that our ideas in the near future must 
undergo fundamental revision. Just at present w^e are unable ta 
specify whether or not the frequent application of these par- 
tially insoluble phosphatic fertilizers is advisable or not. Some 
authors urge that when the crop is to be planted in the spring these 
fertilizers should be applied in the autumn, while some are of the 
opinion that equally good results are obtained by applying them 
at the time of sowing.^* 

Reitmair concludes from his investigations that the extractiorr 
of bones in such a way as to remove practically all of their nitro- 
gen does not unfit them for fertilizing purposes, since the resid- 
ual phosi)liate of lime when reduced to a proper state of fineness, 
is still valuable for its phosphoric acid. 






44 



Reitmair, Wiener landwirtschaftliche Zeitun^^ 1905, 56 : 879, 



889:. 



- \ 



11 



» . 



PART SECOND 



I ! 






NITROGEN IN FERTILIZERS, DRAINAGE WATERS, ETC. 

247. Kinds of Nitrog'en in Fertilizers. — Nitrogen is the most 
costly of the essential plant foods. It has been shown in the first 
volume that the popular notion regarding the relatively great 
abundance of nitrogen is erroneous. It forms only a minute part 
of the matter in and pertaining to the earth's crust. The great 
mass of nitrogen forming the bulk of the atmosphere is inert 
and useless in respect of its adaptation to plant food. It is not 
until it becomes oxidized by combustion, electrical discharges, 
•or the action of certain micro-organisms that it assumes an agri- 
cultural value. 

248 States of Nitrogen. — Having described the relation of nitro- 
gen to the soil in the first volume, it remains the sole province 
of the present part to study it as aggregated in a form suited to 
plant food. In this function nitrogen may claim the attention of 
the analyst in the following forms : 

1. In organic combination in animal or vegetable substances, 
forming a large class of bodies, of which protein may be taken 
as the type. Dried blood or cottonseed-meal illustrates this form 
of combination. 

2. In the form of ammonia or combinations thereof, especially 
as ammonium sulfate, or as amid nitrogen. 

3. In a more highly oxidized form as nitrous or nitric acid, 
usually united with a base of which Chile saltpeter may be 
taken as a type. 

The analyst has often to deal with single forms of nitrogenous 
•compounds, but in many instances may also find all the typical 
forms in a single sample. Among the possible cases which may 
arise, the following are types : 

a. The sample under examination may contain nitrogen in all 
three forms mentioned above. 



^ '4 1 

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^^ AGRICULTURAL ANALYSIS 

b. There may be present nitrogen in the organic form mixed 
with nitric nitrogen. 

c. Ammoniacal nitrogen may replace the nitric in the above 
combination. 

d. The sample may contain no organic but only nitric and 
ammoniacal nitrogen. 

e. Only nitric or ammoniacal nitrogen may be present. 

249- Seeds and Seed Residues.—Thc protcid matters in seeds 
and seed residues, after the extraction of the oil, are highly i^rized 
as sources of nitrogenous fertilizers, either for direct application 
oi for mixing. Typical of this class of substances is cotton- 
seed-meal, the residue left after the extraction of the oil which 
is accomplished at the present time mostly by hydraulic pressure 
but also by the use of a solvent. The residual cakes in the former 
case still contain some oil, but nearlv half their weight consists 
ot nitrogenous compounds. The following table gives the com- 
position of a dry sample of hydraulic pressed cottonseed-meal : 

^J:}^ 760 per cent. 

^'^'^' 4.90 - 

^'^ 10.01 " 

Protein ^^^^ 

Digestible carbohydrates, etc. 26.37 '* 

While the alx)ve shows the composition of a single sample of 
the meal, it should be remembered that there mav be wide varia- 
tions from this standard due either to natural composition or to- 
different degrees of the extraction of the oil. 

The composition of the ash is given below : 

Phosphoric acid, P,0, 31.01 per cent. 

l''';'^'^ ^-^o 35.50 •• 

^^da, Na^o ^ ^^ 

^^""^' CaO 5;68 - 

Magnesia, MgO j^jg m 

vSulfuric acid, SO, 3*^0 .. 

^l'^o\uh\e ^'^^ .. 

Carbon (hoxid and undetermined. 7.46 " 

The cakes left after the expression of the oil from flaxseed- 
and other ody seeds, are also very rich in nitrogenous matters; but 
these res.dues are chiefly used for cattle-feeding and only the- 
und.gested portions of them p,-,.. into the n,anure. Cottonseed 



U i 



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NITROGEN IN SKA- WEEDS 



289 



cake-meal is not so well suited for cattle-feeding as the others 
mentioned, because of the cholin and betain which it contains; 
often in sufficient cpiantities to render its use dangerous to young 
animals. The danger in feeding increases in proportion to the 
total quantity of the two bases and also the relative quantity 
of cholin to betain, the former base being more poisonous than 
the latter. In a sample of the mixed bases prepared by Maxwell 
from cottonseed cake-meal, the cholin amounted to 17.5 and the 
betain to 82.5 per cent, of the whole.'' 

The nitrogen contained in these bases is also included in the 
total nitrogen found in the meal. The actual proteid value of 
the numbers obtained for nitrogen is, therefore, less than that 
obtained for the whole of the nitrogen by the quantity present as 
nitrogenous bases. 

in the United States, cottonseed cake-meal is used in large 
fiuantities as a direct fertilizer, 1)nt not so extensively for mixing 
as some of the other sources of nitrogen. Its delicate yellow 
color serves to distinguisli it at once from the other bodies used 
for similar purposes. No special mention need be made of other 
oil-cake residues. They are quite similar in their composition 
and uses, as well as in their manner of treatment and analysis to 
the cottonseed product. 

250. Nitrogen in Sea-Weeds. The waste available nitrogen finds 
its way sooner or later to the sea, and is recovered therefrom in 
n:any forms. Sea-weeds of all kinds are rich in organic nitrogen. 
Many years ago Forchhanmier pointed out the agricultural value 
of certain fucoids.^« Many other chemists have contributed im- 
portant data in regard to the composition oi these bodies. 

Jenkins has shown from the analyses of several varieties of 
sea-weeds that in the green state they are quite equal in fertiliz- 
ing value to stall manure, and are sold at the rate of ^\e cents 
per bushel.^^ These data are fully corroborated by Goessmann.^« 

Wheeler and llartwell give the fullest and most systematic 

*^ Maxwell, American Chemical Journal, 1891, 13 : 469. 

*« Journal fiir praktische Chemie, 1845, [i], 36 : 385. 

*^ Annual Report of the Connecticut Ivxperinient Station, 1890 : 72. 

*« Annual Report of the Massachusetts ExperinRut Station, 1887 : 223. 



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AGRICULTURAL ANALYSIS 



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discussion which has been pubhshcd uf the agricultural value of 
sea-weeds.'*'* Sea-weed was used as a fertihzer as early as the 
fourth century, and its importance for this purpose has been 
recognized more and more in modern days, especially since chemi- 
cal investigations have shown tlie great value of the food mate- 
rials therein. 

To show the commercial importance of sea-weed, it is only 
necessary to call attention to the fact that in 1885 its value as a 
fertilizer in the State of Rhode Island was $65,044, while the 
value of all other commercial fertilizers was only $164,133. While 
sea-weed, in a sense, can only be successfully applied to marine 
littoral agriculture, yet the extent of agricultural lands bordering 
on the sea is so great as to render its commercial importance of 
the highest degree of interest. 

251. Dried Blood and Tankage. — The blood and debris from 
abattoirs afford abundant sources of nitrogen in a form easily 
oxidized by the micro-organisms of the soil. Blood is prepared 
for use by simple drying and grinding. The intestines, scraps, 
and fragments of flesh resulting from trimming and cutting are 
placed in tanks and steamed under pressure to remove the fat. 
The residue is dried and ground, forming the tankage of com- 
merce. The whole carcasses of animals condemned as unfit- for 
food are reduced to tankage. Dried blood is richer in proteid 
matter than any other substance in common use for fertilizing 
purposes. When in a perfectly dry state it may contain as much 
as 14 per cent, of nitrogen, equivalent to nearly 88 per cent, of 
proteid or albuminoid matter. Tankage is less rich in nitrogen 
than dried blood, but still contains enough to make it a highly 
desirable constituent of manures. 

252. Horn, Hoof and Hair. — These bodies, although quite rich 
in nitrogen, are not well suited to fertilizing purposes on account 
of the extreme slowness of their decomposition. Their presence, 
therefore, should be regarded in the nature of a fraud, l)ecause 
by the usual methods of analysis they show a high percentage of 
nitrogen, and therefore acquire a fictitious value. If these bodies 
be treated with sulfuric acid and rendered soluble their value as 

*^ Rhode Island Experiment vStation, Bulletin 21, 1893. 



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NITROGKN FROM BIRDS 



291 



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'i I 





Fig. 13 ^Vild Ducks and Kgjjfs on Layson Island. 



a manure is greatly increased. The relative value of the nitro- 
gen in these bodies as compared with the more desirable forms, 
lias been a much disputed question. 

• 253. Ammoniacal Nitrogen. — In ammonia compounds, nitro- 
gen is used chiefly for fertilizing purposes as sulfate. Large 
quantities of ammonia are produced in the manufacture of coke 
and in other industrial operations. The ideal nitrogenous fer- 
tilizer is a combination of the ammoniacal and nitric nitrogen 
found in ammonium nitrate. The high cost of this substance 
excludes its use except for experimental purposes. 

254. Nitrogen in Fish,— A large amount of nitrogen is also 
recovered from the sea in fishes. It is shown by Atwater that 
the edible part of fishes has an unusually high percentage of 
protein. ^^ In round numbers about y^ per cent, of the water-free 
edible parts of fish are composed of albuminoids. Some kinds of 
fish, however, are taken chiefiy for their oil and fertilizing value, 
as the menhaden, but the residue after the oil has been extracted 
is even richer in nitrogen than mentioned above. Sciuanto, an 
American Indian, first taught the early New England settlers 
the manurial value of fish.'^^ 

255. Nitrogen from Birds.— Immense quantities of waste nitro- 
gen are further secured, both from sea and land, by the various 
genera of birds. The well known habit of bir(N in congregating 
in rookeries during tlie night and at certain seasons of the yea^r 
tends to bring into a common receptacle the nitrogenous matters 
which they have gathered and which are deposited in their ex- 
crement and in the decay of their bodies. In former times the 
magnitude of these rookeries was probably much greater than now, 
i)nt even at the present time they are of vast extent as shown by 
Fig. 13, a photograph of wild ducks on Layson Island. The feath- 
ers of birds are particularly rich in nitrogen, and the nitroi^enous 
content of the flesh of fowls is also higli. The decav of remains of 
birds, especially if it takes place largely excluded from the leach- 
ing of water, tends to accumulate vast deposits of nitrogenous mat- 
ter. If the conditions in such deposits be favorable to the processes 

^" Report of the Commissioner of Fish and Fisheries, 1888 : 679. 
" Goode, American Naturalist, 1880, 14 : 473. 



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NITROGKN FROM BIRDS 



291 



a manure is greatly increased. The relative value of tlic nitro- 
gen in these bodies as compared with the more desirable forms, 
lias been a much disputed question. 

• 253. Ammoniacal Nitrogen.— In ammonia compounds, nitro- 
gen is used chiefly for fertilizing purposes as sulfate. Large 
quantities of ammonia are produced in tlie manufacture of coke 
and in other industrial operations. The ideal nitrogenous fer- 
tilizer is a combination of the ammoniacal and nitric nitrogen 
found in ammonium nitrate. The high cost of this substance 
exckides its use except for experimental purposes. 

254. Nitrogen in Pish.— A large amount of nitrogen is also 
recovered from the sea in fishes. It is shown by Atwater that 
the edible part of fishes has an unusually high percentage of 
protein.^^ In round numbers about 75 per cent, of the water-free 
edible parts of fish are composed of albuminoids. Some kinds of 
fish, however, are taken chiefly for their oil and fertilizing value, 
as the menhaden, but the residue after the oil has been extracted 
is even richer in nitrogen than mentioned above. Squanto, an 
American Indian, first taught the early New England settlers 
the manurial value of fish.^^ 

255. Nitrogen from Birds.— Immense quantities of waste nitro- 
gen are further secured, both from sea and land, by the various 
genera of birds. The well known habit of birds in congregating 
in rookeries during the night and at certain seasons of the year 
tends to bring into a common receptacle the nitrogenous matters 
which they have gathered and which arc deposited in their ex- 
crement and in the decay of their bodies. In former times the 
magnitude of these rookeries was probably much greater than now, 
l)ut even at the present time they are of vast extent as shown by 
^^g- 13. a photograph of wild ducks on Layson Island. The feath- 
ers of birds are particularly rich in nitrogen, and the nitrogenous 
content of the flesh of fowls is also high. The decay of remains of 
birds, especially if it takes place largely excluded from the leach- 
ing of water, tends to accumulate vast deposits of nitrogenous mat- 
ter. If the conditions in such deposits be favorable to the processes 

*« Report of the Commissioner of Fish and Fisheries, 1888 : 679. 
*^ Goode, American Naturalist, 1880, 14 : 473. 






¥ 



INTENTIONAL SECOND EXPOSURE 



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192 



AGRICULTURAL ANALYSIS 



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of nitrification, the whole of the nitrogen, or at least the larger 
part of it, which has been collected in this debris, becomes 
finally converted into nitric acid and is found combined with 
appropriate bases as deposits of nitrates. The nitrates of the 
guano deposits and of the deposits in caves arise in this way. 
If these deposits be subject to moderate leaching the nitrate 
may become infiltered into the surrounding soil, making it very 
rich in this form of nitrogen. The bottoms and surrounding soils 
of caves are often found highly impregnated with nitrates. 

256. Waste Nitrogen. — When nitrogen has played its role in 
vegetable and animal life it is broken down from the organic 
compounds it has formed by the action of organisms, or in the 
usual processes of decay, and is oxidized again to soluble forms, 
and may be even restored to its gaseous inorganic condition. 

257. Soils Impregnated with Nitrogen. — While for our pur- 
pose, deposits of nitrates only are to be considered which are of 
sufficient value to bear transportation, or to warrant their con- 
centration by leaching, yet much interest attaches to the formation 
ot nitrates in the soil even when they are not of commercial im- 
portance. 

In many of the soils of tropical regions not subject to heavy 
rain-falls, the accumulation of these nitrates is very great. 
Miintz and Alarcano have investigated many of these soils to 
which attention was called first by Humboldt and Boussingault.'- 
They state that these soils are incomparably more rich in nitrates 
than the most fertile soils of Europe. The samples which they 
examined were collected from different parts of Venezuela and 
from valleys of the Orinoco, as well as on the shore of the Car- 
ibbean Sea. The nitrated soils are very abundant in this region 
of South America where they cover large surfaces. Their compo- 
sition is variable, but in all of them carbonate and phosphate of 
lime are met with and organic nitrogenous material. The nitric 
acid is found always combined with lime. In some of the soils 
as high as 30 per cent, of nitrate of lime have been found. Nitri- 
fication of organic material takes place very rapidly the year 
round in this tropical region These nitrated soils are everywhere 

" CoiTiptes rendus, 1885, 101 : 65. 



DEPOSITS OF NITRATES 



293 



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i 



abundant around caves which serve as the refuge of birds and bats, 
as described by Humboldt. The nitrogenous matters, which come 
from the decay of the remains of these animals, form true de- 
posits of guano which is gradually spread around, and which, in 
contact with the limestone and with access of air, suffers com- 
plete nitrification with the fixation of the nitric acid by the lime. 
Large quantities of this guano are also due to the debris of 
insects, fragments of elytra, scales of the wings of butterflies, 
etc., which are brought together in those places by the millions 
of cubic meters. The nitrification, which takes place in these 
deposits, has been found to extend its products to a distance of 
several kilometers through the soil. In some places the quan- 
tity of the nitrate of lime is so great in the soils that they are 
converted into a plastic paste by this deliquescent salt. 

258. Deposits of Nitrates.— The theory of Miintz and Marcano 
in regard to the nitrates of soils, especially in the neighborhood 
of caves, is probably a correct one, but there are many objections 
to accepting it to explain the great deposits of nitrate of soda 
which occur in many parts of Chile and other parts of the world. 
Another point which must be considered also, is this : That the 
process of nitrification can not now be considered as going on with 
the same vigor as formerly. Some moisture is necessary to nitri- 
fication, inasmuch as the nitrifying ferment does not act in perfect- 
ly dry soil, and in many localities in Chile, where the nitrates are 
found, it is too dry to suppose that any active nitrification could 
now take place. 

The existence of these nitrate deposits has long ])ccn known. "^ 
The old Indian laws originally prohibited the collection of the 
salt, but, nevertheless, it was secretly collected and sold. Up to 
the year 182 1, soda saltpeter was not known in Europe except 
as a laboratory product. About this time the naturalist, Mari- 
ano de Rivero, found on the I'acific coast, in the Province of 
Tarapaca, immense new deposits of the salt. Later the salt was 
found in equal abundance in the Territory of Antofogasta, and, 
further to the south, in the desert of Atacama, which forms the 
Department of Taltal. 

*' Journal of the Royal Agricultural Society, 1852, 13 : 349. 



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AGRICULTURAL ANALYSIS 



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At the j)rcsent time the collection and export of saltpeter 
from Cliilc is a business of great importance. The largest ex- 
port prior to 1895, in any one year, was in 1890, when 
the amount ex])()rted was 927,290,430 kilograms; of this quan- 
tity 642,506,985 kilograms were sent to luirope and 86,124,870 
kilograms to the United States. Since that time the imports of 
this salt into the United States have slowly increased. 

The exportations from Chile during the years 1903, 1904 and 
1905 were 1,445,000, 1,480,000 and 1,627,000 tons of 2204 
pounds, respectively. During these three years there were im- 
ported directly into the United States 90,000, 75,000 and 117,000 
tons, respectively.'"* The consumption of nitrate of soda in the 
United States is greater than the direct importation indicates, 
since considerable quantities come into the country from Europe. 
The total consumption in luirope in U)ot, was 1,296,694 tons, 
and in the United States 259,993 tons. The total quantity of the 
salt exported from Chile from 1840 to 1903, inclusive, is 25,947,- 
944 tons. The total quantity produced in Chile in 1905 was 
^733'^>44 tons, three-quarters of which were used as fertilizers. 
Ihe quantity coming to the Ignited States during that year was 
353^^77 tons. The total nitrate production of Chile in 1907 was 
2,100,000 short tons of which 373,988 tons, valued at $13,118,214 
were directly or indirectly imported into the United States. The 
ratio of increase in exportation is rapidly decreasing, having fallen 
from 124 per cent, for the five years 1870-74 to 11.5 per cent, 
for the four years i9oo-03."''^ In 1905 there were 78 factories 
m Chile engaged in the nitrate industry. In order to maintain 
prices a trust of the operators has been formed, regulating the 
amomit which each factory may prwluce. About 55 tons of 
Fait are ])r(Kluced annually for each laborer employed. The price 
per ton to wholesale American consumers ranges from $45 to $53. 
It is estimated that at the present rate of consumption, ihe sup- 
ply from Chile will rapidly diminish in aI)out 20 years.*^® 

According to Pissis these deposits are of very ancient origin. 

" L'Kiigrais, 1906, 21 : 35. 

^•' American Fertilizer, 1905, 22:5. 

^« American Fertilizer, 1905, 22 : 6. 



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THE NITER DEPOSITS OF CALIFORNIA 



295 



4), 

CM 



This geologist is of the opinion that the nitrate deposits are the 
result of the decomposition of feldspathic rocks; the bases thus 
produced gradually becoming united with the nitric acid pro- 
vided from the air.^^ 

According to the theory of Nollner, the deposits are of more 
modern origin and due to the decomposition of marine vegeta- 
tion.^^ Continuous solution of soils gives rise to the formation 
of great lakes of saturated water, in which occur the develop- 
ment of much marine vegetation. On the evaporation of this 
water, due to geologic isolation, the decomposition of nitrogen- 
ous organic matter causes generation of nitric acid, which, coming 
in contact with the calcareous rocks, attacks them, forming nitrate 
of calcium, which, in presence of sulfate of sodium, gives rise to 
a double decomposition into nitrate of sodium and sulfate of 
calcium. 

The fact that iodin is found in greater or less quantity in 
Chile saltpeter, is one of the chief supports of this hypothesis of 
marine origin, inasmuch as iodin is always found in sea and not 
in terrestrial plants. Further than this, it must be taken into 
consideration that these deposits of nitrate of soda contain neither 
shells nor fossils, nor do they contain any phosphate of lime. 
The theory, therefore, that they are due to animal origin, is 
scarcely tenable. 

Extensive nitrate deposits have been discovered in the U. S. 
of Columbia."'^ These deposits have been found extending 
over 30 square miles and vary in thickness from one to 10 feet. 
The deposits consist of a mixture of sodium nitrate, sodium 
chlorid, calcium sulfate, aluminum sulfate and insoluble silica, • 
and contain from one to 13.5 per cent, of nitrate. 

259 The Niter Deposits of California.— Many of the condi- 
tions which favor the deposition of niter in the soil are found in 
Southern California ami Arizona, and it has been confidently 
predicted that niter deposits of value and of great extent would 
be found in these localities. The California vState Mining Bureau 

" I'uchs and de Launay, Traits des Gites min^raux, 1S93, 1 : 425. 

^ Le Feuvre and Dagnino, El Salitre dc Chile, 1893 : 12. 

** Wiley, Presidential Address, Journal of the American Chemical 
Society, 1894, 16 : 20. 



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has made investigations of the deposits of niter in Southern CaH- 
fornia, and has collected practically all of the exact information 
that is available on the subject.*^" Nearly ail of the niter deposits 
which have been discovered up to the present time are found in 
the northern part of San Bernardino County, and the beds arc 
found particularly along the shore lines, or old beaches that 
mark the boundary of Death Valley as it doubtless appeared 
ounng the eocene times. The beds and clays contain the de- 
posits which have been worn by erosive agencies into knobs, 
buttes and ridges that have been compared by some to haystacks 
and potato hills. 

I'ntil lately the principal value of the niter hills was sup- 
posed to lie solely in the surface coating. When this is removed, 
deposits which are full of other saline compounds are exposed. 
This top coating is, in accordance with the custom followed in 
Chile, called by the Spanish name ''caliche." This caliche ranges 
in depth from a few inches to several feet. The surface caliche 
evidently owes its deposits of salt to the upward capillary flow 
of water from below% induced by the rapid evaporation at the 
surface in a region comparatively devoid of rains. The niter 
deposit is in the form of a soluble salt, which readily permeates 
the clay and separates into a white crystalline deposit. In Chile 
the colors of the caliche are usually yellow, pink and green, but 
in California a creamy yellow is the characteristic color ; though 
pinks and greens are sometimes found. The quantity of niter 
contained in the caliche is extremely minute as compared with 
the more concentrated deposits of Chile, and hence it is evident 
that these extensive deposits in California will not become avail- 
able commercially, until the more concentrated deposits in Chile 
and (.ther similar localities are exhausted. The chief difficulty in 
the California deposits is that the niter is associated with other 
soluble salts, chiefly common salt, from which it is with some 
difficulty separated. The following table gives typical examples 
of the composition of the soluble salts of the caliche, not the 
representative or mean composition, but the extreme types of 
samples containing various proportions of niter: 

^ California State Mining Bureau, Bulletin 24, 1902 : 154. 



FUNCTIONS OF SODIUM NITRATE 297 

'^345 

Niter (NaNO,) 7.28 14.50 27.40 46.50 61.20 

Chlorid of vSodium 6.36 7.56 21.15 25.30 16.40 

Sulfate of Sodium .60 .70 2.05 5.30 3.10 

Sulfate of Lime .20 .10 1.04 .30 .20 

Sulfate of Magnesium.. . 1.30 2.80 2.00 1.20 1.20 

Insolubles 84.26 74.34 46.36 21.40 17.90 

100.00 100.00 TOO.OO 100.00 100.00 

It was found that the average composition of 104 samples 
of caliche, taken from as many different claims, was 9.54 per cent, 
of niter. The quantity of niter which has been located in South- 
ern California is difficult to estimate. The following estimate 
comprises the whole amount of niter which is thought to exist 
in the small areas surveyed, but it does not indicate what can 
be commercially extracted. About 35,000 acres of the deposit 
have been examined, in which it is estimated that there exi.st 
about 22,000,000 tons of nitrate of soda. This, of course, is only 
a very rough estimate and is perhaps of little value in basing- 
computations of the future supply. 

In general, it may be said that the niter beds of California are 
at the present time of little importance from a cominercial point 
of view\ Not only is the amount of niter comparatively small, 
but the distance from markets and the cost of transportation 
are so great as to practically exclude the product from the mar- 
kets of the world. 

It is stated by Pennock that no commercial success has at- 
tended the exploitation of nitrate deposits in the United States.«^ 
According to the same author the production of nitrate of soda 
IS practically confined to Chile. 

260. Functions of Sodium Nitrate.— Practically the only form 
of oxidized nitrogen which is of importance from an agronomic 
point of view is sodium nitrate, often known in commerce by 
the name Chile saltpeter. Ammom'acal compoimds and nitrites 
are usually oxidized to nitric acid or its compounds before they 
are assimilated as plant foods. Applied to a growing crop, sodium 
nitrate at once becomes dissolved at the first rainfall or by the 
natural moisture of the .soil. It carries thus to the rootlets of 
*' lournal of the American Chemical Society, 1906, 28 : 1248. 



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ACRICUI,TL'R-\L ANALYSIS 



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plants a supply of nitrogen in the most hii^hly available state. 
There is perhaps no other kind of plant food which is offered to 
the living vegetable in a more completely predigested state, and 
none to which a quicker response will be given. By reason of 
its high availability, however, it must be used with care. A too 
free use of such a stimulating food may have, in tlie end, an 
injurious elYect upon the crop, and is quite certain to lead to the 
waste of a considerable i)ortion of expensive material. For this 
reason sodium nitrate should be ai)f)lied with extreme care, in 
small (juantities at a time, and only when it is needed by the 
growing crop. It would be useless, for instance, to apply this 
fertilizer in the autumn with the expectation of its benefiting 
the crop to a maximum degree the follow^ing spring. Again, if 
the api)lication of this salt should be made just previous to a 
heavy rain, almost or quite the whole of it would be removed 
beyond the reach of the absorbing organs of the plant. 

W hen once the nitric acid has been absorbed by the living 
rootlet it is held with great tenacity. Living plants macerated 
in water give up only a trace of nitric acid, but if they be pre- 
viously killed with chloroform, the nitric acid they contain is 
easily leached out. 

The molecule of sodium nitrate is decomposed by dissociation 
or otherwise in the ])rocess of the absorption of the nitric acid. 
The acid enters the ])lant organism and the soda is left to combine 
with the soil acids. The nascent soda may thus pl^ a role of 
some importance in decomposing particles of minerals contain- 
ing potash or phosphoric acid. Some authorities sav the decom- 
position of the sodium nitrate takes place in the cells of the ab- 
sorbing plant organs, for it is difficult to understand how it 
could be accomplished externally. While the soda, therefore, is 
of no importance as a direct plant food, it can hardly be dis- 
missed as of no value whatever in the process of fertilization. 
Many of the salts of soda, as, for instance, common .salt, are rpiitc 
hygroscopic and serve to attract moisture from the air and thus 
become carriers of water between the plant and the air in sea- 
.sons of drought; and sodium nitrate itself is so hygroscopic as 
not to be suited to the manufacture of gunpowder. 



IM •« 



ADULTERATION OF CHILE SALTPETER 



299 



To recapitulate: The chief functions of sodium nitrate are to 
give to the plant a supply of oxidized nitrogen ready for absorp- 
tion into its tissues and incidentally to aid, by the residual soda, 
in the decomposition of silt particles containing potash or phos- 
phoric acid and in sui)plying to the soil salts of a more or less 
deliquescent nature. 

261. Commercial Forms of Chile Saltpeter.— The Chile salt- 
peter of commerce may reach the farmer or analyst in the lumpy 
state in which it is shipped, or as finely ground and ready for 
application to the fields. Unless the farmer is provided with 
means for grinding, the latter condition is much to be preferred. 
It permits of a more even distribution of the salt, and thus en- 
courages economy in its use. For the chemist also it is advan- 
tageous to have the finely ground material, which condition per- 
mits more easily a perfect sampling, a process which, with the 
unground salt, is attended with no little difficulty. 

262. Percentage of Nitrogen in Chile Saltpeter.— Chemically 
pure sodium nitrate contains 16.49 per cent, of nitrogen. The 
salt of commerce is never pure. It contains moisture, potash, 
magnesia, lime, sulfur, chlorin, iodin, silica and insoluble mate- 
rials, and traces of other bodies. The value of the salt depends, 
therefore, not only on the market value of nitrogen at the time 
of sale, but also on its content of nitrogen. The nitrate of com- 
merce varies greatly in its nitrogen content and is sold on a 
guaranty of its purity. The best grades range in nitrogen from 
15 to 16 per cent. The content of nitrogen has long been esti- 
mated in the trade by determining the other constituents and 
counting the rest as nitrogen. This practice arose in former 
times wdien no convenient method was at hand for determining 
nitric nitrogen. The process is tiresome and unreliable, because 
all errors of every kind are accumulated in the nitrogen content, 
but inasmuch as the method is still required by many merchants, 
the analyst should be acquainted with it, and it is therefore given 
further along. The usual methods for determining nitric nitro- 
gen may be applied in all cases where samples of sodium nitrate 
are under examination, but some special processes are described 
further on for convenience. 

263. Adulteration of Chile Saltpeter.— The analyst, aside from 



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AGRICULTURAL ANALYSIS 



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the honesty of the dealer, is the only protector of the farmer in 
guarding against the practice of adulteration of sodium nitrate. 
Even the honest dealer is compelled to protect himself against 
fraud, and therefore, the world over, commerce in this fertilizer 
is now conducted solely on the analyst's certificate. Happily, 
therefore, adulteration is almost unknown, because it is certain 
to be detected. Formerly, the saltpeter was adulterated with 
common salt, or low grade salts from the potash mines ; but it 
is an extremely rare thing now to find any impurities in the salts 
other than those naturally present. 

In every case the analyst may grow suspicious when he finds 
the content of nitrogen in a sample to fall below 13 per cent. It 
must not be forgotten, however, that some potassium nitrate may 
be present in the sample, and since that salt contains only 13.87 
per cent, of nitrogen, its presence would tend to lower the value 
of the fertilizer; but although the potash itself is a fertilizer of 
value, it is not worth more than one-third as much as nitrogen. 
]n all cases of suspected adulteration, it is advisable to make 
a complete analysis. The results of this work will, as a rule, 
lead the analyst to a correct judgment. 

264. The Application of Chile Saltpeter to the Soil.— The 
analyst is often asked to determine the desirability of the use of 
sodium nitrate as a fertilizer and the methods and times of ap- 
plying it. These are cjuestions which are scarcely germane to 
the purpose of this work, but which, nevertheless, for the sake 
of convenience, may be briefly discussed. In the first place, it 
may be said that the data of a chance chemical analysis will not 
afford a sufficiently broad basis for an answer. A given soil 
may be very rich in nitrogen as revealed by chemical analysis, 
and yet poor in an available supply. This is frequently the case 
with vegetable soils, containing, as they do, large quantities of 
nitrogen, but holding it in practically an inert state. T have 
found such soils very rich in nitrogen, yet almost entirely devoid 
of nitrifying organisms. It is necessary, therefore, in reaching a 
judgment on this subject from analytical data to consider the 
different states in which the nitrogen may exist in a soil, and 
above all, the nitrifying power of the soil if the nitrogen be 



B ; 



UTILIZATION OF^ NITROGEN 



301 



chiefly present in an organic state. Culture solutions should 
therefore be seeded with samples of the soil under examination 
and the beginning and rapidity of the nitrification carefully noted. 
In conjunction with this the nitrogen present in the soil in a nitric 
or ammoniacal form should be accurately determined. 

The quantities of Chile saltpeter which should be applied per 
acre vary with so many conditions as to make any definite state- 
ment impossible. On account of the great solubility of this salt, 
no more should be used than is necessary for the nutrition of the 
crop. For each 100 pounds used, from 14 to 15 pounds of nitro- 
gen will be added to the soil. Field crops, as a rule, will require 
less of the salt than garden crops. There is an economic limit 
to the application which should not be passed. As a rule, 250 
pounds per acre is a maximum dressing for field crops. The 
character of the crop must also be considered. Different amounts 
are required for sugar beets, tobacco, wheat, and other standard 
crops. It is rarely the case that a crop demands a dressing of 
Chile saltpeter alone. It will give the best effects, as a rule, when 
applied with phosphoric acid or potash. But this is a branch of 
the subject which cannot be entered into at greater length in 
this manual. The reader is referred to Weitz's work on Chile 
saltpeter for further information. ^^ 

265. The Utilization of Nitrogen in the Air as a Fertilizing^ 
Material. — The only form of plant which has developed these tu- 
bercles to any extent is the legumes. It is, therefore, commonly 
understood that the nitrifying organisms of symbiotic forms are 
confined to leguminous plants. At the same time, mention is made 
in Volume I of the possible direct nitrifying of atmospheric nitro- 
gen without the intervention either of any organic form thereof, 
or the activity of other symbiotic nitrifying activity. Some of 
the results of earlier workers in this field seem to indicate the 
existence of organisms which are capable of directly nitrifying 
atmospheric nitrogen and making it available as a fertilizing 
material. These earlier ideas which are mentioned in Volume I, 
have of late years received further investigation, with the result 
of establishing more firmly the belief that nitrification, indepen- 

^'^ Der Chilisalpeter als Diingeniittel, 1905. 



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AGRICULTURAL ANALYSIS 



dent of the processes commonly associated therewith, may some- 
times take place. "^ 

^i'he iiitluence of oxid of iron in the soil in rendering available 
the nitrogen of the air, has received special attention. Bonnema 
has given to this subject careful consideration and has come to 
the conclusion that the so-called fixation of atmospheric nitrogen 
in the soil is dependent upon the presence of ferric hydroxid. 
This substance appears to have the property of oxidizing ele- 
mental nitrogen and changing it into nitrous acid, which is capa- 
ble of conversion into nitric acid in the usual manner. 

It appears from this investigation that the first step in the 
nourishment of a ])lant by atmospheric nitrogen is not necessarily 
one of biological chemistry, but rather one of a simple elementary 
process.^* 

This problem has lately been studied more closely by Sestini.'''^ 
It appears from the investigation made by Sestini that it is not 
the elemental nitrogen of the air, but the ammonia which is con- 
tained therein which is oxidized by ferric hydroxid into nitric acid. 
This is an important observation in view of the fact that it is 
generally supposed that the ammonia which enters the soil from 
the air is converted into nitrous acid through the activity of nitri- 
fying ferments. The utilization of the oxid of iron, therefore, is 
liot directed to the increase of the total (quantity of assimilable 
nitrogen, but only to the change of the ammonia into an assimi- 
lable form. This has an important bearing upon the study of 
the chemical ])rocesses relating to fertilizing materials by reason 
•of the relation of ammonia to fertility. The highly beneficial ef- 
fects i)roduced by the application of ammonia salts have long 
been recognized. Most observers claim that these salts are only 
useful when converted into nitric acid, and others that they arc 
useful in the absence of ferments which can produce this change. 
In either case, however, it is evident, in view of the observations 
above mentioned, that ammonia is not directly assimilable even 

" Wiley, Principles and Practice of Agricultural Analysis, 2n(l Edition, 
1906, 1 : 568. 

^^ Cluniiker-Zeitunji;, 1903, 27 : 149. 

Die landwirLschaftlichen Versuchs-Stationen, 1904, 60 : 103. 



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UTILIZATION OF ATMOSPHERIC NITROGEN 



303 



in the cases last mentioned, but only after being converted into a 
more highly oxidized form by the activity of ferric hydroxid. 

It seems to be established that ferric hydroxid at ordinary 
temperature, that is, from 15° to 25°, develops a catalytic 
infiuence on ammonia and ammonia salts, and that under this 
influence an assimilable form of nitrogen is developed in the soil 
independently of the activity of nitrifying ferments, even in the 
presence of large quantities of thymol or of corrosive sublimate 
up to two per cent., quantities which are entirely sufficient to 
inhibit the action of the ordinary nitrifying ferments. The am- 
monia of the air and of the soil may thus be converted into nitrous 
acid by the oxidation produced under the influence of the catalytic 
activity of ferric hydroxid. 

266. The Utilization of Atmospheric Nitrog-en by Other Plants 
Than Legumes.— The evidence which seeks to establish the fact 
that other plants than legumes are capable of utilizing atmos- 
pheric nitrogen is not wholly conclusive. Theoretically, it seems 
a rather strange provision of nature that only i)lants of the legu- 
minous family should have the faculty, either symbiotically with 
nitrifying organisms or directly, to utilize atmospheric nitrogen 
as a source of plant food. Nevertheless, the greater number of 
carefully conducted experiments in which all sources of possible 
error are excluded, have led, as a rule, to negative results with 
other plants, so that it can scarcely be aflirmed with any scientific 
certainty that this property of i)lants is a general or even a com- 
mon one. On the other hand, m a review of this subject in con- 
nection with research work, Jamieson has reached the conclusion 
that the property of utilizing atmospheric nitrogen belongs to 
many other forms of plants besides the legumes."^ In this re- 
port Jamieson undertakes to establish the fact that the legtime 
tubercle theory is untenable, and that the nitrogen of the air is 
directly utilized by plants in general. In all the plants examined 
by him, structures which absorb free nitrogen from the air and 
transform it into the organic state were found. Seventeen forms 
of plants of widely difi'erent character arc said by Jamieson U) 
have been examined and foimd to possess the property indicated. 

*« Report of the Agricultural Research Association of the North- 
ea.stern Counties of Scotland, 1905 : 16. 



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AGRICULTURAL, ANALYSIS 



The i)lants which are least ca])ahle of utiHzing atmospheric nitro- 
gen are the monocotyledons, and especially the cereals and grasses. 
According to Jamieson, the chlorophyll cell seems to possess 
in a high degree the property of transforming nitrogen, and the 
function of the green cell, in this particular, is analogous to that 
possessed by it of utilizing the carbon of the carbon dioxid 
in the air for the purpose of producing organic compounds. He 
claims to have estahlislied the fact, that the free nitrogen in the 
air is directly absorbed and transformed into organic compounds 
by these cells. 

The number of these organs, their nature, and their apti- 
tude to exercise their functions vary consideral)ly from one plant 
to another. Jn particular, the monocotyledons such as the cereals 
and grasses are very i)oorly endowed with the organs from the 
point of view of the fixation of nitrogen. The form of these 
organs also varies greatly and the different forms observed by 
Jamieson are described in his work. These organs are called 
producers of protein, and are not met with in general except in 
the tender part of the very young leaves or their petioles. At 
the beginning of their formation they do not contain any pro- 
tein. When these organs are completely developed the produc- 
tion of protein begins and the organs are sometimes gorged with 
protein, and this continues for a certain length of time. The 
plants which are most apt to fix a great deal of nitrogen do not 
have need of nitrogen fertilizers, provided they find at the begin- 
ning of their development favorable conditions that will permit 
the proper growth of the organs which produce the i)rotein. In- 
stead of buying nitrogenous fertilizers as a greater aid to the 
plants which are able to fix only little nitrogen, such as cereals 
and grasses, it will be sufficient to cultivate those plants which 
absorb and fix a great deal of nitrogen and thus to incorporate 
this nitrogen in the soil. 

These observations are cited solely to call attention to them. If 
confirmed by future investigations, they wili prove useful in prac- 
tical agriculture in securing a more abundant supply of nitrogen- 
ous material for plant growth. 

267. Accumulation and Utilization of Atmospheric Nitrogen 
in the Soil.— Interesting investigations have been made on this 




ATMOSPHKRIC NITROGI^N IN THE SOIL 



305 



11 



point by Voorhees and Lipman.^^ The experiments conducted were 
so arranged as to bring out the relation of leguminous crops, 
such as cow peas, to soil and nitrogen and to determine, as far 
as practicable, the value of this leguminous crop as a source of 
nitrogen to subsequent non-leguminous crops. The soils selected 
contained an abundance of phosphoric acid and potash. The 
facts established by the investigation are of practical importance, 
in respect of the possibility of accumulating nitrogen in the soil 
directly from atmospheric nitrogen. The greater number of the 
investigations were of negative value, but a sufficient positive gain 
was found in some cases to indicate that further investigation may 
develop methods to promote the fixation of nitrogen in the soil. 
The authors admit that the probability of the continued fixation 
of nitrogen, in the manner in which the investigations were made, 
is not very great. Attention is called to the fact, however, that 
the present knowledge of bacteriological conditions in the soil is 
still so limited, that a general and successful inoculation with 
non-symbiotic nitrogen-fixing bacteria is out of the question. 
There is also a danger to be avoided in the attempt to increase 
the soil nitrogen by means of the inoculation of leguminous plants, 
where large quantities of leguminous material are incorporated 
in the soil, as shown by researches above mentioned. The nitro- 
gen-decomposing bacteria can develop freely and the denitrifying 
organisms may set free more nitrogen than the nitrifying organ- 
isms fix. 

Therefore, the practical problem of the utilization of atmos- 
pheric nitrogen as a fertilizing material is to be considered, and 
the conditions which determine the comparative rate of nitrifi- 
cation and denitrification are to be carefully studied in order that 
valuable results may be reached. 

The authors also found that even under carefully controlled 
conditions there was no uniform gain of nitrogen due to the 
inoculation of soils with nitrifying ferments.''* 

The investigation shows that there was no decided gain in 
nitrogen in the inoculated soil after the inoculation. There was, 
*' Journal of the American Chemical vSociety, 1905, 27 : 556. 
«*New Jersey State Agricultural Kxperiment Station, 25th Annual Re- 
port, 1904 : 239. 



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AGRICULTURAL, ANALYSIS 



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Rf 



in all cases, a loss or nitrogen during the summer when the soils 
were kept bare, and the losses were greatest where manure had 
been used. 

These data show that the ])rohlem of increasing soil nitrogen 
in a uniform manner through the oxidation of atmospheric nitro- 
gen is still unsolved. There is probably no other one problem 
of greater importance to agriculture. The nitrogenous fertilizers 
are of dominant importance, both by reason of their high cost and 
of the necessity of their i)resence in order that the other fertil- 
izing materials in the soil shall be duly utilized. There are many 
indications, however, that m the near future the method for the 
utih'zation of atmospheric nitrogen by direct oxidation thereof 
in the field, either with or without the aid of growing plants, 
may be discovered and thus the farmer made more independent 
of the nitrogen now stored in various parts of the earth or pro- 
duced by manufacturing operations. 

268. Manufacture and Use of Cyanamid for Fertilizing Pur- 
poses.— Cyanamid has the general formula ILN : CN. With 
univalent metals it yields metallic compounds corresponding to 
j\IoN:CN. In investigating the manufacture of cyanids by 
means of carbids, Frank and Caro observed that if moist atmos- 
pheric nitrogen be passed through a retort heated to dull redness 
and containing a nn'xture of calcium and barium carbids, the 
nitrogen becomes fixed to the metal with formation of cyanid ; 
besides cyanid, other nitrogenous compounds, e. <^., cyanamid, 
due in part to the action of the cyanid already formed and in 
part to the direct action of the reacting mass, as the following 
equations indicate, are formed :''••• 

X(2MCX)+XX=X(M.,NCN)-f(CN)X 
MX,+ X,=M,XCXfC 

The formation of cyanamid may be increased by giving the 
carbid a large surface thus allowing a large amount of nitrogen to 
act upon a small cpiantity of carbid. Frank and Caro's process 
is based on this observation. 

The process of the Deutsche Gold und Silber Scheide Anstalt 

Tr^^r.^?!?'"^ """"^ I.enKleii, The Cyanid Industry, Translated bv LeClerc, 
1900, . 144. 



1 



CYANAMID COMPOUND AS A FERTILIZER 



307 



'in 
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for the preparation of cyanamid uses carbon in the solid state or 
in the form of hydrocarbon gas, and an alkali amid; or NH^ 
brought in contact w^ith a melted alkali metal and charcoal at 
400°-6cx)°. In this way, alkali amid is formed which under the 
action of a portion of the charcoal becomes alkali cyanamid."'* 

Calcium cyanamid (the formula of which when ]nire is CaCNo) 
is a black powder, resembling basic slag in other properties and 
containing over 20 per cent. N, readily soluble in HoO, besides 
more or less CaO, CaCo and C. 

Gerlach found it to be equal in mamnial value to XaXO.^ 
and (NHJ2SO4 in pot experiments with barley and white mus- 
tard, though in field experiments its value fell to 74 (NaNOa^ 
100).^^ With peaty soils, calcium cyanamid acts injuriously, due 
probably to the formation of dicyanodiamid by the organic acids, 
unless the application of the manure be made five or six wrecks 
before sowing. 

This early application causes a loss of nitrogen, wdiich should 
be taken into account in reckoning its value. 

Otto found it nearly as efficacious as sodium nitrate when 
used with spinach or cabbage, and better than nitrate or annnoni- 
acal nitrogen in fertilizing maize.''^^ 

Hall in comparing it with ammonium sulfate for fertilizing 
mangels, swedes and mustard, obtained favorable results."'^ 

The best way to determine the nitrogen in calcium cyanamid is 
to digest it with strong sulfuric acid by the usual kjeldahl process. 

CaCN^ decomposes in the soil into CaCO^ and NH, ; this 
makes the soil alkaline; therefore it ls better to use acid phos- 
phate than disodium phosphate.^* 

269. Cyanamid Compound as a Fertilizer. — Experiments have 
been conducted by Shutt and Charlton at the agricultural ex- 
periment station at Ottawa to determine the value of cyan- 
amid compound as a fertilizer. The effect of the compound 

^^ Robine and Lenglen, The Cyanid Industry, Translated by LeClerc, 
1906: 176. 

^' Biederniann's Central-Blatt, 1904, 33 : 649. 

"' Chemisches Central-Blatt, 1905, I : 117. 

" Journal of A^jricultural Science, 1905, 1 : 146. 

^* In iinura, Bulletin of the College of Agriculture, Tokyo, 1906, 7 : 53. 



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AORICULTURAL ANALYSIS 



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upon the vitality of seeds was first studied. The resiilt of these 
experiments was to show that the cyanamid comixmnd, except 
in very minute quantities, injuriously affected the vitality of the 
seed. As the amount is increased the toxic effect becomes more 
and more noticeable, not only in the retardation of germination, 
but also upon the health and vigor of the young plant. Wheat is 
better able to resist this action than ])eas. Nevertheless the wheat 
plants in the tests which contained the larger amount of cyanamid 
frequently turned black, withered and died after reaching a 
height of from three to f\VG inches. It is believed that cyanamid 
compound in amounts not greater than fiYQ milligrams of nitro- 
gen to 100 grams of soil, does not prove injurious to the germina- 
tion of seed. Toxic effects were markedly noticeable, on the 
other hand, with amounts of cyanamid containing between 10 
and 12 milligrams of nitrogen per 100 grams of soil. The potas- 
sium compound appears to be more injurious in action upon the 
life of the seed and young plants than the calcium salt. In regard 
to the value of cyanamid compound as a fertilizing material, the 
experiments were confined to the study of its degree of nitrifica- 
tion. It would seem from a consideration of the data secured that 
as the comparative amount of the cyanamid compound is increased 
in the soil there is a corresponding decrease in the rate of nitrifi- 
cation. This is probably due, as already indicated, to the toxic ac- 
tion ui)on the nitrifying organisms. It may be due partly also to 
denitrifying changes leading to a reduction of a part of the 
nitrogen to the free state. The conversion of the nitrogen of the 
cyanamid into available forms is probably continuous under 
favorable conditions, though not uniformly so. The first stage of 
the i)rocess may be considered possibly as purely chemical, since 
water at ordinary temperatures converts the nitrogen of cyan- 
amid into ammonia. Further changes are brought about 
through the agency of living organisms, and are necessarily slow- 
er, depending for their activity on many factors, prominent among 
which is the relative proportion of the cyanamid compound 
present in the soil.'-'^ 

270. Later Experiments with Cyanamid.— Grandeau has sum- 
" Chemical News, 1906, 94 : 150. 



II 



LATER EXPERIMENTS WITH CYANAMID 



309 



marized the latest results of the experimental value of nitrate 
and cyanamid of calcium produced by the electric process des- 
cribed later. '^ The compound used by him was produced by a 
factory in Norway, the term "Norwegian Nitrate" being used to 
distinguish it from the nitrate of Chile. The calcium cyanamid 
when subjected to the moisture of the soil produces ammonia. 

The commercial product contains from 20 per cent, to 22 per 
cent, of nitrogen, while the sulfate of ammonia contains about 25 
per cent. Pure calcium cyanamid CNoCa, contains 35 per cent, 
of nitrogen. The commercial cyanamid is a black powder, ground 
extremely fine, which owes its color to the carbon which it con- 
tains, in all about 17 per cent. 

Practical experiments made by Cart, and reported to Grandeau, 
show that while the nitrate of lime acted very successfully as a 
fertilizer, the cyanamid of calcium was somewhat disappointing. 
There was difficulty in spreading this brown and black powder 
regularly, and in applying it to the soil the fine powder was ex- 
tremely irritating to the face and hands. The effect upon the 
wheat after 24 hours was described as being similar to that pro- 
duced by a solution of sulfate of copper, while the wheat treated 
with the nitrate took on a beautiful green tint and grew rapidly, 
and that which had received the cyanamid turned to a reddish 
tmt, which was retained for at least a week. 

The total amount of wheat harvested from the plot receiving 
the cyanamid was less than that receiving no nitrogenous fertili- 
zer at all. 

Miintz and Nottin conclude that the calcium cyanamid does 
not interfere with germination when employed in ordinary quan- 
tities, not exceeding 200 kilograms per hectare, and gives good 
results. 

It is possible that the deleterious effects of the calcium cyan- 
amid may be due to the fact which has been noticed by investi- 
gators that in tlic manufacture of cyanamid it may be associated 
with another compound, viz., dicyanamid, the poisonous proper- 
ties of which for plants are well known. Perhaps the poisonous 
action noticed above by Cart may have been due to such an ad- 
mixture. The matter needs further investicration. 

^^ Journal (rAgricuUurL> pratic^ue, 1908, 72 : 229. 



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271. utilization of Atmospheric Nitrogen.— In the first vol- 
uiiic of this w(jrk attention has been called to the fixation and 
utilization of atmospheric nitrogen by the action of bacteria, 
•especially those hvin^,^ in symbiosis with lej^uminous plants."^ Ber- 
thelot in the first volume of his Vegetable and Agricultural Chem- 
istry, has set out at great length the various methods in which 
atmospheric nitrogen may be rendered available for agricultural 
purposes/'^ It will prove convenient for the analyst and student 
to have a summary of the clif^crent methods described in which 
atmospheric nitrogen may be rendered useful for plant food. 
The methods as set forth by iJerthelot are as follows: 
(i) Fixation of atmospheric nitrogen by means of microbes 
in the earth and upon vegetables. 

(2) The continued fixation of free nitrogen by the organic 
compounds under the iuHuence of atmospheric electricity of feeble 
tension. 

(3) The fixation of nitrogen under the influence of slow oxi- 
<Iation. 

There are many subdivisions made under these various heads 
but those represent in general the principal methods which Ber- 
thelot has studied. All these methods, it is noticed, are purely 
natural, that is, those which are going on constantly in nature, 
Berthelot not having taken up the study of the artificial production 
of nitrogen under strong electric influences in the first volume 
of his work. 

272 Historical Development of the Fixation of Atmospheric 
Nitrogen by Means of Electricity.-The principal steps^ in the de- 
velopment of the investigation looking to the fixation of atmos- 
pheric nitrogen have been traced by Erlwein.^^ Attention is 
called to the researches of Crookes, Lord Rayleigh, Bradlev 
Lovejoy, Birkeland, Kowalsky, and Pauling in the research' 
work and practical application of the i)rinciples discovered Spe- 
cial attention is given to the' work done by Siemens 
and llalske. These investigators studied the problem of 
the production of nitric acid by electrical discharges between 
1906; 1 52^; ^""^>P^^^ ^-^ ^''--ctice of Agricultural Analysis, 2ncl Edition. 

'"Chimie v<^jr^taleet a^rirole. 1899. 1 
Klektrotechnische Zeitschrift 1007 1 d. < r a^ -cm ^ t • , 
and Metallurgical Industry, 19^7 6 : 77 ^^ ^'' ^2. Electrochemical 



ATMOSPHERIC NITROGEN BY MEANS OF EI^CTRICITY 3 II 



heavy carbon electrodes. They also utilized the horn lightning 
arrester consisting of two vertical horns, the lower ends of which 
are near together, while upwards the two horns diverge from 
each other more and more. The arc is formed between the two 
lower ends of these electrodes and travels upwards, thereby en- 
larging its surface and causing it finally to be automatically bro- 
ken. None of these methods, however, resulted in securing oxi- 
dized nitrogen on a commercial scale. The development of the 
cyanamid furnace is fully described in this paper and the funda- 
mental reaction by which calcium cyanamid is produced is given 
as CaO -f 2C H- 2N = CaCN^ + CO. When the price of cal- 
cium carbid fell to a point at which it could be commercially used 
it was found that the production of calcium cyanamid was more 
economically secured by starting with the carbid itself. The 
fundamental reaction in this case is CaCo-|-No=CaCN^-|-C. 
The princii)le of the construction of the cyanamid furnace is 
based upon the utilization of a series of coal-fired retorts, closed 
air-tight, and partially filled with powdered calcium carbid. After 
the contents of the retort have reached a white heat nitrogen gas 
is introduced therein. In these conditions the carbid rai)idly ab- 
sorbs the nitrogen. The reaction is exothermic and the heat 
evolved promotes still more the activity of the combination. Af- 
ter the carbid is absorbed by the nitrogen the incandescent cyan- 
amid is removed from the retorts, cooled under exclusion of the 
air and powdered and packed for shipping. 

The commercial calcium cyanamid is a black |x:)wder, quite 
stable in the air and consists of 57 per cent, of calcium cyanamid 
14 per cent, free carbon, to which the black color is due, 21 per 
cent, caustic lime, 2^ per cent, of silicic acid, four per cent, of 
iron oxid, and small ciuantities of sulfur, ])hosphorus and carbonic 
acid. The average content of nitrogen is about 20 per cent. 
When placed in water calcium cyanamid dissolves, decomposing 
quickly, especially in hot water, and yielding caustic lime, and, 
by polymerization, a complicated compound called dicyanamid. 
Subjected to overheated steam calcium cyanamid gives off its 
nitrogen quantitatively in the form of ammonia. Tn aqueous 
solution, under the influence of certain acids, a series of synthetic 
organic compounds are produced, among which is found urea. 



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When fused with sodium carbonate, sodium chiorid or other 
similar materials, all of the nitropcn in the cyanamid is converted 
into cyaiiid nitrogen, in other words, the product is a mixture 
of calcium cyanid, and sodium cyanid. Erlwein draws the 
following conclusions from the present state of the art: 

Cyanamid may be used directly as a fertilizer in agricul- 
ture. Those who are interested in the agricultural side of the 
problem will find interesting comparative pictures of the growth 
of plants under the fertilizing action of Chile saltpeter and cal- 
cium cyanamid, etc., in the original Cerman paper. 

2. Calcium cyanamid may be used for the production of ammo- 
nium sulfate, which is also consumed in large quantities for fer- 
tilizing purposes. The reaction yielding ammonia is CaCN -+- 
3li,0=CaC()3+2NH3. 

3. Cyanamid may bo used for the manufacture of dicyanainid 
a compound used in iIk- manufacture of anilin dyes and gun 
powder. J5y suitable leaching with water and crystallization 
this compoun.l is obtained in the form of pretty white crystals The 
chemical equation is 2CaCN,+4H,0=2Ca(OH),+ (CNNHj.,. 

4- Cyanamid may be used as the starting material for the coin- 
inercial manufacture of sodium cyanid or potassium cyanid Ac- 
cording to a process <levised by Freudenberg, the calcium is 
incited with .so.hum chiorid in excess and is thereby transformed 
almost completely into sodium cyanid. The product obtaine.l in 
this way, which contains about 22 to 23 per cent, of sodium cy- 
anid correspon.ling to 30 per cent, of potassium cyanid), is either 
sold directly in this form as so-called "sodnun-cyanid substitute" 
(Cyannatrium-Surrogat) for use in gold metallurgy, or is worked 
up in o chemically pure .sodium cyanid or potassium cyanid. 
Roth bran.ls will be ma.le on a commercial scale as soon as a 

new factory is completed which is in course of erection near 

licrliii. 

5. As a hardening material for iron and steel, calcium cyan- ' 
fs"dl r riy "Z '^^'''' "^ application. This application 

ron which IS thereby hardened. ITnis ability is enhanced by the 
a<ld„ion of other compounds to the cyanamid and this product is 



PRODUCTION OF NITRIC ACID BY ELECTRIC ACTION 



313 



111 



now sold under the trade name of ''Ferrodiir." Dr. Reininger, 
chief chemist of the well-known tool-steel and machine works of 
Ludwig Loewe, first recognized this property of cyanamid and 
called attention to the extremely uniform action of this new 
hardening material, which proves useful especially at such tem- 
peratures at which a uniform introduction of carbon into iron 
heretofore met with difficulties. 

6. For the manufacture of urea a small plant is already in 
operation in which the calcium cyanamid is treated in a suitable 
way with acids and immediately changed into solutions of urea, 
which may be easily crystallized. 

273. Production of Nitric Acid by Electric Action. — This sub- 
ject has been largely studied in many parts of the world, 
and in this country at Niagara Falls works of consid- 
erable magnitude have been erected for the production of nitric 
acid under electric influence, the electric power being generated 
by the water of Niagara Falls. '»"* 

The Atmospheric Product Company at Niagara Falls installed 
upon the methods of Bradley and Lovejoy gave, at first, api)ar- 
ently satisfactory results per kilowatt in the production of nitric 
acid. This method, however, necessitated apparatus of a very 
complicated character in order to insure its industrial success. 
For this reason, since the summer of 1904 it has not been operated 
for the production of nitric acid. The company had hoped to 
utilize 1 50,000-horse i)ower furnished by Niagara Falls, 
and expected, therefore, to make a sufficient quantity of 
nitrate of soda for the world's supply. It is possible 
that the time may come when the utilization of 1 50,000- 
horse power will accomplish this result, but the experience so 
far obtained at Niagara does not bear out the hopes of its im- 
mediate fulfilment. While these experiments were conducted at 
Niagara Falls, Kowalski and Moscicki built a factory at Frilx^urg 
for the manufacture of nitric acid by electricity. They used 
alternating currents of very high tension, from 50 to 75 thou- 
sand volts. The electrodes employed were of alumiiumi. This 
factory, however, does not appear to have had very much 
greater success commercially than the one at Niagara Falls. 

79a Grandeaii, La Production ^lectri(iiie de I'Acide nitri(iue, 19(^6. 



1 ; 



I 



314 



AGRICULTURAL ANALYSIS 









t * > 



Hf 






4 



In TQ03 an improvcnuMit in the manufacture of nitric acid 
from the atmosj)here was made hy Birkeland and Eyde. IJirke- 
land employed a continuous current produced by 40 amperes at 
600 volts, which, in connection with other principles of the method, 
produced a maj^netic field of very ^reat intensity. This led to the 
invention and establishment of the apparatus which lias been 
erected at Notodden, Norway. The furnaces now constructed com- 
prise three of identical structure. The energy of the furnace has 
been carried from 500 to 700 kilowatts, that is from 700 to 1000 
horse power, for each of them. It has been possible, in the very 
latest experiments to increase the energy of these furnaces to 1500 
horse power. It is found, however, that the furnaces work more ef- 
fectually and give better results at a uniform utilization of from 
500 U) fx)o kilowatts. The electric energy necessary for the work- 
ing of the factory at Notodden is furnished at a j^rice of 32 francs 
I)er kilowatt-year. The electricity is furnished by a generator 
of two thousand kilowatts capacity of a triphase construction and 
at a tension of 5000 volts. The air sent into the furnace by the 
ventilators is used up at the rate of 25,000 liters per minute for 
each one, that is for the three furnaces 75,cxx) liters per minute. It 
at once reaches the magnetic field formed by the wall of the fur- 
nace made of fire clay. The air mixed with the nitric gas pro- 
duced in the furnace leaves the apparatus through a tul)e kepi 
at a temperature of from 500° to 7oo^ a temperature much 
higher than that in other apparatus destined to produce nitric acid. 
The gases pass first through a tubular boiler where they are cooled 
to about 200^ The steam which is produced In' this boiler 
is utilized 111 the concentration of the solutions of nitrate of lime 
which are finally formed. From this boiler the gases are intro- 
duced into the cooling apparatus which rapidlv reduces their tem- 
perature to .so° or 60". a temperature which is the most 
favorable to the reactions which result in the formation of nitrous 
acid. In the magnetic field of the furnace it should be under- 
stood that there is formed only a single nitrogen combination ; 
namely, oxid of nitrogen NO. Its proportion reaches about 
five per cent, of the total volume of gas. At a very high tempera- 
ture of from 2000° to 2500° the elements of this oxid* are separa- 



II 



ABSORPTION TOWERS 



315. 



led and recombinecl incessantly in such a way that the total 
percentage of the oxid of nitrogen remains constant in the mix- 
ture. 

274. Oxidation Towers. — These large reservoirs comnumicate 
with the electric furnaces by large tubes and are two in number. 
They are cylindrical in shape and in the interior are covered by 
a material which is not attacked by acids. In these towers the 
further oxidation of the oxid of nitrogen produced in the furnace 
takes place. In a short time in these towers the oxid of nitrogen 
(NO) is converted into NOo. Leaving the reservoirs, the nitrous 
gas produced is forced through a ventilator into the absorption 
towers where it is transformed into nitric acid. The transforma- 
tion which takes place in these last towers, converts the nitrous 
oxid into nitric acid by means of water according to the formula, 
2NO,-f HoO=HNO,-f HNO,. At the same time that the nitric 
and nitrous acids are formed there are produced lower oxids of 
nitrogen by the decomposition of nitrous acid according to the 
following equation: 2HNOo=NOo+NO-f H2O. These are re- 
oxidized by the continuous fundamental reaction. 

275. Absorption Towers. — These are prismatic in shape, having 
a section four meters square and 10 meters high. They con- 
lain, therefore, 40 cubic meters. They are placed along the sides 
of a hall in two parallel ro^ws, each row embraces two towers in 
granite and two towers in sandstone, filled with pieces of quartz 
of the size of the thumb, two-thirds of their height. In the in- 
terior of these towers there are circulated in an inverse direc- 
tion and in a continuous manner the gases and the water. This 
water, which constantly moistens the quartz, is charged pro- 
gressively with the nitric acid which is formed. The other nitrous 
products, with the exception of the lower oxids, which accompany 
the formation of nitrous acid, are reoxidized in these towers in 
contact with the oxygen of the air, and give new quantities of 
nitrous acid, as has just been described. Finally, when the solu- 
tion of nitric acid produced in the towers has attained by re- 
peated contact with the gases and water a concentration of 50 
per cent., that is, 50 kilograms of monohydrated nitric acid in 
100 liters of liquid, it is received into ordinary vessels made of 



1 > 



i 



316 



AGRICULTURAL ANALYSIS 



MANUFACTURE OF NITRATE OF LIME 



317 



! ! 



^n 






■1 ! 


; 
• « 


S 


i 


i ' 



granite and provisionally stored therein. From the towers in 
which the water and gases coming from the oxidation towers 
are circulated in an inverse direction, there is obtained the 
greatest part of the nitrate product transferred into nionohydrate 
nitric acid and dissolved in water, ft is, however, very import- 
ant not to permit the loss of the nitric products which have es- 
caped absorption in the system of towers and are found in nota- 
ble quantities in the gases escaping from the last one of the ves- 
sels. In order to collect these gases an energetic absorbent is 
used, namely, milk of lime. For this purpose there is a fifth tower 
of wood of the same dimensions as the first four, and this is fillea 
with bricks disposed in layers and over which circulates, method- 
ically distributed, the milk of lime. The nitrous and nitric gases 
are retained by the lime and produce a mixture of nitrite and 
nitrate of lime. This mixture is afterwards broken up by the 
aid of nitric acid into the nitrate of lime and gaseous nitrous oxid, 
which is reintroduced into the absorbent system in the manner 
which has already been described. This breaking up of the com- 
pound by means of nitric acid is expressed by the following equa- 
tion : (CaNO,),-fHN03=r(CaN03),+H,0-fNO,-fNO. 

Finally, in order to complete the operation and retain the rest 
of the nitric gases which still escape from the milk of lime vessel, 
these gases are made to traverse another vessel somewhat 
smaller in dimension than the other and containing quickHme. 
Jt is only in escaping from this last vessel that the gases which 
have traversed the whole system of oxidation since their entry 
mto the electric furnace are allowed to escape into the atmos- 
phere. The operations which have just been descril^ed permit 
the final transformation into pure nitric acid of '50 per cent, 
strength, of at least 95 per cent, of the oxid of nitrogen producer! 
m the electric furnace, a remarkable result for an industrial opera- 
tion. 

276. Manufacture of Nitrate of Lime.-The solution of pure 
nitrate of lime, coming from the decomposition of mixtures of 
nitrates and nitrites descril)ed above, is conducted, together with 
the pure nitric acid of 50 per cent, strength, into a row of open 
vessels of granite containing pieces of carbonate of lime of from 



13 to 20 centimeters in diameter. The carbonate of lime is em- 
ployed in quantities suitable to neutralize completely the acid 
solution and to produce neutral nitrate of lime. This operation 
is conducted methodically in four superimposed vessels. Upon 
the fresh carbonate the solution which has been almost neutralized 
is brought. The fresh acid is placed in contact with the residue 
of lime wdiich has not been dissolved by the first treatments with 
the partially saturated solution. By reason of their superposition 
the movement of the liquid in the vessels is operated automat- 
ically. P'inally, there is obtained a solution of neutral nitrate of 
lime which is conducted into evaporation vessels. The concen- 
tration of the liquid is accomplished partially by the aid of steam 
coming from the boiler used for the cooling of gases escaping 
from the electric furnace, as has been previously described, and 
I)artially in a direct manner. The solution of nitrates is reduced 
to such a concentration that their boiling point rises to 145 '^j 
which gives a liquid containing from 75 to 80 per cent, of nitrate 
of lime, equivalent to from 15.2 to 15.5 per cent, of nitrogen. 
This viscous mixture is poured into vessels of 200 liters capacity 
and allowed to solidify by cooling. Tlie nitrate can be shipped 
•either in this state or after powdering. 

Instead of evaporating the nitrate of lime until the liquid 
has obtained a boiling point of 145°, it may be allowed to crys- 
tallize after having been evaporated to 120° only. The crystals of 
nitrate of lime are then separated in a centrifugal. Finally there 
is manufactured at Notodden some basic nitrate of lime by 
adding to the hot solution a proper proportion of quicklime. 
After cooling, the product is broken up and passed through a 
sieve. The basic nitrate contains about 10 per cent, of nitrogen. 
It: goes without saying that by the process just described there 
can also be manufactured nitrate of soda, or potash, in place of 
nitrate of lime. It is the cheapness of the lime, however, as com- 
pared with soda which has led the manufacturers at Notodden 
to transform the nitric acid into calcium nitrate. 

The actual production of nitric acid at Notodden amounts to 
from 500 to 600 kilograms per kilo watt-> ear. The factory, which 
has been running since the 2d of May, i</)5, has produced in one 



I 



1'^ 



•3i8 



AGRICULTURAL ANALYSIS 



ABSORPTION OF NITRIC ACID 



319 



year 730,000 kiloj^^rams of monohydratc nitric acid. The success 
of this enterprise, which has been so anxiously awaited throughout 
the whole world, should lead the farmers of the world to enter- 
tain the hope that even if the stores of nitric acid in Chile and 
other localities are exhausted there can be created a supply of 
this material, which may be said to be unlimited, obtained from 
the air and ofYered from an inexhaustible source, not only for 
agricultural needs, but also other industrial needs of man. 

It is not likely that this process of Birkeland and Eyde has 
yet reached its limit of perfection. There is no reason why 
some similar process might not be conducted in connection with 
the great waterfalls of this country, which would lead to a su[)- 
ply of nitric acid even at a lower price than can now be secured 
from natural stores. 

277. Absorption of Nitric Acid and Concentration of the Product. 
—This subject is discussed still further by Howies, espe- 
cially in regard to the direct oxidation of nitric acid in the air by 
means of electric discharges and the production of nitric acid 
therefrom without the intervention of the calcium compounds. 
The conclusions reached by Howies in regard to this method 
of producing nitric acid are as follow^s :^" 

After leaving the furnace, the air contains about two per cent. 
i)y volume of nitric oxid, which becomes rapidly converted, by 
means of the excess oxygen present into nitrogen peroxid. 
The mixed gases then pass on to absorption towers, which present 
no special features of construction and down which water or 
dilute acid flows. Tn the case of the last tower, milk of lime is 
nsed, as it is difficult to absorl) the last traces of NO., by means 
of water alone. J^ this process there is obtained an 'acid of 
not more than 50 per cent, strength. 

The preparation of a concentrated nitrous-free acid from the 
nitrous gases constitutes one of the most serious problems in 
connection with this process. The reaction represented by this 
equation, viz., 2N0,+0+H,0=r.2HN0,, does not take place 
m the absorption towers; such an equilibrium appears to exist 
only m the gaseous state. On condensation the right-hand side 

^ Electrochemical and Metallurgical Industry, 1907, 6 : 358. 



of the equation is not produced. The most concentrated acid 
which has so far been obtained by the condensation of nitrous 
gases in water in the presence of oxygen corresponds to the for- 
mula HNO.^, 2H2O, and possesses a density of 40.6"^ B., repre- 
senting 63.63 per cent, of anhydrous nitric acid. The forma- 
tion of this acid takes place, according to the following equation, 
in the Lunge and Rohrmann plate towers : 

2NO,-fO+5H,0=2(HN03, 2HX)), 

from which acid of 40° to 41 '^ B. is obtained. l)y passing the 
gases, however, through towers down which water flows, an 
equimolecular mixture of nitric and nitrous acids results, which 
at the most, can not attain a concentration greater than that 
obtained in the Lunge tow^ers. Attempts at further concentra- 
tion by the passage of nitrogen peroxid through the solution, 
simply result in an increase of nitric acid at the expense of the 
nitrous. The strongest acid is thus never free from nitrous 
acid, and each succeeding absorption tow^er contains less and 
less nitric acid, while at the same time the nitrous acid in- 
creases, for as the free oxygen in the gases becomes consumed 
the NO and NO^ tend to react as N.O.,, yielding only nitrous 
acid. It is not possible to prepare much stronger acid by frac- 
tionating the 50 per cent, acid from the first absorption tower, 
since a product of mininumi vapor pressure, boiling at 120^, 
and containing 68 per cent, of anhydrous acid, is obtained as 
residue. 

Thus in order to prepare the most concentrated acid by the 
nitrogen combustion process it would be necessary to either 
add the 50 per cent, acid to concentrated sulfuric acid until a 
"dilution of say 54° B., is obtained (54° B. ecpials 120° Tw. 
-equals 68.5 per cent, of HoSOJ, and distill the nitric acid; or to 
prepare a salt of nitric acid, and distill in the usual way with 
sulfuric acid or a bisulfate. 

An electrolytic method for concentrating and oxidizing the 
•weak tower acid has lately been patented. The process con- 
sists in refrigerating the oxids of nitrogen evolved during elec- 
trolysis at the cathode, and leading them in the liquid state slow^- 
ly to the anode compartment of the cell, where in presence of 



320 



AGRiCULTURAI, ANALYSIS 



the nascent oxygen there generated, a sohitlon of pure nitric acid 
results, all nitrous acid undergoing oxidation. It is not stated 
if this process has proved a commercial success. 

Thus, although the electrochemical production of nitric acid 
has attained a fair degree of efficiency in some of the processes 
described, the problem of directly manufacturing a 98 per cent, 
acid from the furnace gases has not yet been solved. 

278. Method of Moscicki.— A further contribution to this in- 
teresting subject from an agricultural point of view has been 
made by Moscicki. ^^^ In the system of Moscicki the ])rinci])le of 
the magnetic deflection of the arc is used. The ^tudy of a 
quiet flame shows different zonef within the flame. Only the 
hottest zone is usQ^*{6r the oxidation of the nitrogen. The 
oxidized nitrogen which is produced within this hot zone is 
more or less decomposed in passing into the parts of the arc 
of lower temperature. The important modification of Moscicki, 
therefore, consists in suppressing these cooler areas, and this is 
accomplished by a magnetic deflection of the flame. The mag- 
netic attraction only sets those parts of the flame into motion 
which carry the electric current, while on account of the rapidity 
of the motion the influence of the cooler zones is eliminated. 

279. Production of Nitric Acid in the United States from At- 
mospheric Nitrogen.— The present status of the industries relat- 
ing to the oxidation of atmospheric nitrogen and the produc- 
tion of nitric acid, or some similar product therefrom, in the 
L-nited States may still be described as a waiting one. There 
is no doubt of the importance of the problem under considera- 
tion, esi)ecially to agriculture, but the actual economical devel- 
opment of the industry is still in the future. Two general 
methods of experimental work have been followed. One class 
of experiments looks to the use of electric discharges through 
the air in order to produce the oxidation of the nitrogen and 
form the first ])roducts, which afterwards may be developed 
into nitric acid.^- 

As has been before intimated the electric plant established at 

" p:iectrocheinical and Metallur/^ncal Industry, 1907, 5 : 491. 
" Klectrocheinical and Metallurgical Industry, 1907, 5 : 289. 



I- 



CLASSIFICATION OF METHODS 



321 



Niagara Falls for the production of nitric acid from the air 
has been abandoned. The success of the experiments in Norway 
IS promising, but attention is called to the fact that the process 
in Norway utilizes the moving arc method instead of the old 
spark method, and is dependent essentially on the exceedingly 
low^ prices of electric power in that country. 

'i1ie second method of utilizing the atmospheric nitrogen, 
which is now under investigation, is that which starts with cal- 
cium carbid, the product of the electric furnace, and treats 
this compound later with nitrogen in such a way as to produce 
the calcium cyanamid. A company has been formed in the 
United States to operate a factory upon the above principle, and 
it is proposed to erect a plant of 20,000 metric tons annual 
capacity on the Tennessee River in Northern Alabama. In this 
locality there is abundant and cheap water power, as well as 
coal and coke. Labor is also abundant and reasonably cheap, 
'llie Tennessee River also furnishes water transportation of the 
cheapest character. It is near some of the great phosphate 
deposits, so that in the manufacture of the complete fertilizers 
a large part of the material would be derived from the same 
localities. 

METHODS OF ANALYSIS 
280. Classification of Methods— In case a microscopic exam- 
ination of the sample is re(|uire(l it should precede the chemical 
operations. In general, there are three direct methods of deter- 
mining the nitrogen content of fertilizers. First the nitrogen 
may be secured in a gaseous form and the volume thereof, under 
standard conditions, measured and the weight of nitrogen com- 
puted. This process is commonly known as the absolute method. 
Practically it has passed out of use in fertilizer work, or is prac- 
ticed only as a check against new and untried methods, or on 
certain nitrogenous compounds which do not readily yield all 
their nitrogen by the other methods. The process, first perfected 
by Dumas, whose name it bears, consists in the combustion of 
the nitrogenous body in an environment of copper oxid, by which 

the nitrogen, by reason of its inertness, is left in a gaseous state 
II 



f 



322 



AGRICULTURAI, ANALYSIS 



OFFICIAL METHODS 



323 



after the oxidation of the other constituents; viz., carbon and 
hydrogen, originally present. 

In the second class of methods the nitrogen is converted into 
ammonia, which is absorbed by an excess of standard acid, the 
residue of which is determined by subsequent titration with a 
standard alkali. There are two distinct processes belonging to 
this class, in one of which ammonia is directly produced by dry 
combustion of an organic nitrogenous compound with an alkali, 
and in the other ammonium sulfate is produced by moist com- 
bustion with sulfuric acid, and the salt thus formed is subse- 
quently distilled with an alkali and the free ammonia resulting 
therefrom estimated as above described. Nitric nitrogen may 
also be reduced to ammonia by nascent hydrogen either in an 
acid or alkaline vSolution. 

In the third class of determinations is included the estimation of 
nitric nitrogen by colorimetric methods. These processes have 
little practical value in connection with the analyses of com- 
mercial fertilizers, but find their chief use in the detection and 
estimation of extremely minute quantities of nitrites and nitrates. 
In the following paragraphs will be given the standard methods 
for the detenm'nation of nitrogen in practical work with fertiliz- 
ing materials and fertilizers, and also the methods for the esti- 
mation of minute quantities of ammoniacal and nitric nitrogen. 

281. Determination of the State of Combination.— Some of 
the sample is mixed with a little powdered soda-lime. If am- 
moniacal nitrogen be present free ammonia is evolved even in 
the cold and may be detected either by its odor or by testing 
the escai)ing gas with litnnis or turmeric paper. A glass rod 
moistened with strong hydrochloric acid will produce white 
tumes of ammonium chlorid when brought near the escaping 
ammonia. , 

If the sample contain any notable amount of nitric acid it will 
be revealed by treating an acjueous solution of it with a crystal 
of ferrous sulfate and strong sulfuric acid. The iron salt should 
be placed in a test-tube with a few drops of the solution of the 
fertilizer and the sulfuric acid poured down the sides of the tube 
in such a way as to run under and not to mix with the other 



liquids. The tube must be kept cold. A dark brown ring will mark 
the disk of separation between the sulfuric acid and the aqueous 
solution in case nitric acid be present. If water produces a 
solution of the sample too highly colored to be used as above, 
alcohol of 80 per cent, strength may be substituted. The colora- 
tion produced in this case is of a rose or purple tint. 

Nitric nitrogen may also be detected by means of brucin. If 
a few drops of an aqueous solution of brucin be mixed with the 
same quantity of an aqueous extract of the sam])lc under exam- 
ination and strong sulfuric acid be added, as described above, 
there will be developed at the disk of contact between the acid 
and the mixed solutions a persistent rose tint varying to yellow. 

To detect the presence of albuminoid nitrogen the sample is 
exhausted with water and heated with soda-lime, which gives 
rise to ammonia which may be detected as described above. 

282. Microscopic Examination. — If the chemical test reveal 
the presence of organic nitrogen, the next point to be determined 
is the nature of the substance containing it. Often this is 
revealed by simple inspection, as in the case of cottonseed-meal. 
Frequently, however, especially in cases of finely ground mixed 
goods, the microscope must be employed to determine the charac- 
ter of the organic matter. It is important to know whether 
hcu'r, horn, hoof, and other less valuable forms of nitrogenous 
compounds have been substituted for dried blood, tankage, and 
more valuable forms. In most cases the qualitative chemical, and 
microscopic examination will be sufficient. There may be cases, 
however, where the analyst will be under the necessity of using 
other means of identification suggested by his skill and expe- 
rience or by the circumstances connected with any particular in- 
stance. In such cases the general appearance, odor, and consis- 
tence of the sample may afiford valuable indications which will 
aid in discovering the origin of the nitrogenous materials. 

283. Official Methods. — The methods adopted by the Asso- 
ciation of Official Agricultural Chemists have been developed 
by more than 20 years of co-operative work on the part of the 
leading agricultural chemists of the United States. These meth- 
ods should be strictly followed in all essential points by all analysts 



iBP' 



324 



AGRICUI.TURAl, ANALYSIS 



OFKICIAL VOLUMKTRIC METHOD 



in cases where comparison with other data is concerned. Future 
experience will doubtless improve the processes both in respect 
of accuracy and simplicity, but it must be granted that, as at 
present practiced, they give essentially accurate results. 

284. Volumetric Estimation by Combustion with Copper Oxid. 
■—This classical method of analysis is based on the principle, that 
by the combustion of a substance containing nitrogen in copper 
oxid and conducting the products of the oxidation over red-hot 
copper oxid and metallic copper, all of the nitrogen present in 
whatever form will be obtained in a free state and can subse- 
' quently be measured as a gas. The air originally present in all 
parts of the apparatus must first be removed either by a mer- 
cury pump or by carbon dioxid, or by both together, the resid- 
ual carbon dioxid being absorbed by a solution of caustic alkali. 
Great delicacy of manipulation is necessary to secure a perfect 
vacuum, and, as a rule, a small quantity of gas may be measured 
other than nitrogen, so that the results of the analyses are often 
a trifle too high. The presence of another element associated 
with nitrogen, or the possible allotropic existence of that ele- 
ment, may also prove to be a disturbing factor in this long prac- 
ticed, analytical process. For instance, if nitrogen be contaminated 
with another element, e. o., argon, of a greater densitv, the com- 
monly accepted weight of a liter of nitrogen is too great and 
tables of calculation based on that weight would give results 
too high. 

First will be given the official method for this process, fol- 
lowed by a few simple variations thereof, as practiced in the 
laboratory of the Bureau of Chemistry. 

285. The Official Volumetric Method.-This process may be 
used for nitrogen in any form of combination. Practically ' it is 
no longer used in fertilizer analysis, but the method is inserted 
here because of its historic and scientific value. 

The apparatus and reagents needed are as follows : 

Combustion tube of best hard Bohemian glass, about 66 centi- 
meters long and 12.7 millimeters internal diameter. 

Acotomctcr of at least 100 cubic centimeters capacity, accu- 
rately calibrated. 



325 



Sprcngel mercury air-pump. 

Small paper scoop, easily made from stiff writing paper." 

Coarse cupric oxid, to be ignited and cooled before using. 

Fine cupric oxid, prepared by grinding ordinary cupric oxid 

Metallic copper, granulated copper, or fine copper gauze, 
heated and cooled in a current of hydrogen. 

Sodium bicarbonate, free from organic matter. 

Caustic potash solution, a supersaturated solution of caustic 
potash m hot water. When absorption of carbon dioxid during 
the combustion ceases to be prompt, the solution must be re- 
placed with a fresh portion. 

Filling the tube.~Vse from one to two grams of ordinary 
commercial fertilizers. In the case of highly nitrogenized sub- 
stances, the amount to be used must be regulated bv the amount 
of nitrogen estimated to be present. Fill the tube as follows : ( i ) 
About five centimeters of coarse cupric oxid. (2) Place on the 
small paper scoop enough of the fine cupric oxid to fill after 
having been mixed with the substance to be analyzed about 10 
centimeters of the tube ; pour on this the substance, rinsing the 
watch-glass with a little of the fine oxid, and mix thoroughly 
with a spatula ; pour into the tube, rinsing the scoop with a little 
fine oxid. (3) About 30 centimeters of coarse cupric oxid. (4) 
About seven centimeters of metallic copper. (5) About six 
centimeters of coarse cupric oxid (anterior layer) (6) A 
small plug of asbestos. (7) From eight-tenths to one gram of 
sodium bicarbonate. (8) A large, loose plug of asbestos. Place 
the tube in the furnace, leaving about two and five-tenths centi- 
meters of it projecting; connect with the pump by a rubber stop- 
per smeared with glycerol, taking care to make' the connection 
perfectly tight. 

Operation.— Exhaust the air from the tube bv means of the 
pump. When a vacuum has been obtained, allow the flow of 
mercury to continue; light the gas under that part of the tube 
containing the metallic copper, the anterior layer of cupric oxid 
(see (5) above), and the sodium bicarbonate. As soon as the 
vacuum is destroyed and the apparatus filled with carbon dioxid, 
shut oii the flow of mercury and at once introdtice the delivery 



if? 



i'i! 



;!■ 



€ St 



326 



AGRICULTURAL ANALYSIS 



THE PUMP 



Z'^l 



tube of the pump into the receiving arm of the azotometer just 
below the surface of the mercury seal, so thai tlie escaping bub- 
bles will pass into xn^ air and not into the tube, thus avoiding 
the useless saturation of the caustic potash solution. 

When the flow of carbon dioxid has very nearly or completely 
ceasl'd, ])ass the delivery tube down into the receiving arm, so that 
the bubbles will escape into the azotometer. Light the gas under 
the 30 centimeter layer of oxid, heat gently for a few moments to 
drive out any moisture that may be present, and bring to a red 
heat. Meat gradually the mixture of substance and oxid, lighting 
one jet at a time. Avoid a too rapid evolution of bubbles, which 
should be allowed to escape at the rate of about one per second 
or a little faster. 

When the jets under the mixture have all been turned on, 
light the gas under the layer of oxid at the end of the tube. 
When the evolution of gas has ceased, turn out all the lights 
except those under the metallic copper and anterior layer of 
oxid, and allow to cool for a few moments. Exhaust with the 
pump and remove the azotometer before the flow of mercury is 
stopped. Break the connection of the lube with the pump, stop 
the flow of mercury, and extinguish the lights. Allow the azo- 
tometer to stand for at least an hour, or cool with a stream of 
water until a permanent volume and temperature have been 
reached. 

Adjust accurately the level of the potassium hydroxid solution 
in the bulb to that in the azotometer; note the volume of gas, 
temperature, and height of barometer; make calculation as usual, 
or read results from tables. 

286. Note on Official Volumetric Method. — The determina- 
tion of nitrogen in its gaseous state by combustion with copper 
oxid, has practically gone out of use as an analytical method 
The official chemists rarely use it even for control work on sam- 
ples sent out for comparative analysis. The method recom- 
mended differs considerably from the process of Jenkins and 
Johnson, on which it is based. The only source of oxygen in 
the official method is in the copper oxid. Hence it is necessary 



that the oxid in immediate contact with the organic matter be in 
a sufficiently fine state of subdivision, and that the substance 
itself be very finely powdered and intimately mixed with the 
oxidizing material. Failure to attend to these precautions will 
be followed by an incomplete combustion and a consequent deficit 
in the volume of nitrogen obtained. 

The copper oxid before using is ignited, and is best filled into 
the tube while still warm by means of a long pointed metal scoop, 
or other convenient method. The copper spiral, after use, is re- 
duced at a red heat in a current of hydrogen, and may thus be 
used many times. 

287. The Pump.— Any form of mercury pump which will 
secure a complete vacuum may be used. A most excellent one 
can be arranged in any laboratory at a very small expense. The 
pump used in the laborator>- of the Bureau of Chemistry for 
many years answers every purpose, and costs practically nothing, 
bemg made out of old material not very valuable for other use! 

The construction of the pump and its use in connection with 
the combustion tul>e will be clearly understood from the follow- 
ing description : 

A glass bidb I is attached, by means of a heavv rubber tube 
carrying a screw clamp, to the glass tube A, having heavy walls 
and a small internal diameter, and being one meter or more in 
length. The tube A is continu d in the form of a U, the two 
arms being joined by very heavy rubber tubing securely wired. 
The ends of the glass tubes m the rubber should be bent so that 
they come near together and form the bend of the U, the rubber 
simply holding them in place. This is better than to have the 
tube continuous, avoiding danger of breaking. A three way tube, 
T, made of the same kind of glass as A, is connected by one arm,' 
a, with the manometer B, by a heavy rubber union well wired' 
The union is made perfectly air-tight by a tube filled with mercury 
held in place by a rubber stopper. The middle arm of the tee 
a', is expanded into a bulb, E, branching into two arms, one of 
which is connected with A and the other with the delivery tube 
F, by the mercury-rubber unions, MM', just described. The in- 



:ii 



■■ur- 



328 



AGRICULTURAL ANALYSIS 



VOLUMETRIC METHOD 



329 






terior of the bulb E should be of such a shape, as to allow each 
drop of mercury to fall at once into F without accumulating in 
large quantity and being discharged in mass. The third arm of 
the tee, a", is bent upwards at the end and passes into a mercury 
sealing tube, D, where it is connected by means of a rubber tube 
with the delivery tube from the furnace. The flow of the mer- 




Fig. 14. Mercury Pump and Azotometer. 



cury is regulated by the clamp C, and care should be taken that 
the supply does not get so low in I as to permit air bubbles to 
enter A. The manometer B dips into the tube of mercury H. 
A pump thus constructed is simple, flexible, and perfectly tight. 
The only part which needs to be specially made is the three way 
tube T, and the one in use here was blown in our own laboratory. 
The bent end of the delivery tube F may also be united to the main 



tube by a rul)])er joint, thus aiding in inserting it into the V- 
shaped nozzle of the azotometer. 

The azotometer used is the one devised by Schifif and modified 
by Johnson and Jenkins.*'^ 

The V nozzles may be got separately and joined to any 
good burette by a rubber tube. The water-jacket is not neces- 
sary, but the api)aratus can be left exposed until it reaches room 
temperature. 

Any form of mercury pump capable of securing a vacuum 
may be used, but the one just described is commended by sim- 
])licity, economy, efifectiveness, and long use. 

288. The Pump and Combustion Furnace.— The pump and 
combustion furnace, as used in the above process, are shown in 
Fig. 14. The pump is constructed as just described, and rests in 
a wooden tray which catches and holds any mercury which may 
be spilled. The furnace is placed under a hood which carries 
off the products of the burning gas and the hot air. A well 
ventilated hood is an important accessory to this process, espe- 
cially when it is carried on in summer. A small mercury pneu- 
matic trough catches the overflow from the pump and also serves 
to immerse the end of the delivery tube during the exhaustion 
of the combustion tube. 

The other details of the arrangement and connections have 
been sufficiently shown in the previous paragraph. 

289. Volumetric Method of Bureau of Chemistry.— Tt has been 
found convenient to vary slightly the method of the official 
chemists in the following respects : The tube used for the com- 
bustion is made of hard refractory glass, which will keep its shape 
at a high red heat. It is drawn out and sealed at one end after 
being well cleaned and dried. It should be about 80 centime- 
ters in length and from 12 to 14 millimeters in internal diameter. 
The relative lengths of the spaces occupied by the several con- 
tents of the tube are approximately as follows: Sodium bicar- 
bonate, two ; asbestos, three ; coarse copper oxid, eight ; fine copper 
oxid, containing sample, 16 ; coarse copper oxid, 25 ; spiral copper 

"American Chemical Journal, 1880-81, 2 : 27. 



'A 

t 



m 



"^ 



I 



II 



330 



AGRICUI^TURAL ANALYSIS 



gauze, 10 to 15; copper oxid, eight; and asbestos plug, five centi- 
meters, respectively. 

The cop])er oxid should be heated for a considerable time to 
redness in a muffle with free access of air before using, and the 
copper gauze be reduced to pure metallic copper in a current of 
hydrogen at a low red heat. The anterior layer of copper oxid 
serves to oxidize any hydrogen that may have been occluded by 
the copper. When a sample is burned containing all or a con- 
siderable ])art of the nitrogen as nitrates, the longer piece of cop- 
per gauze is used. 

290. The Combustion. — The tube having been charged and 
connected with the pump, it is first freed from air by running the 
pump until the mercury no longer rises in the manometer. The 
end of the tube containing the sodium bicarbonate is then gently 
heated, so that the evolution of carbon dioxid will be at 
such a rate, as to slowly depress the mercury in the manome- 
ter, but never fast enough to exceed the capacity of the pump to 
remove it. The lamp is extinguished under the sodium car- 
bonate and the carbon dioxid completely removed by means of 
the pump. The delivery tube is then connected' with the azotom- 
eter, and the combustion tube carefully heated from the front 
end backwards, the copper gauze and coarse copper oxid being 
raised to a red heat before the part containing the sample is 
reached. W hen the nitrogen begins to come off, its flow should 
be so regulated by means of the lamps under the tube, as to be 
regular and not too rapid. From half an hour to an hour^hould 
be employed in completing the combustion. Since most sam- 
ples of fertilizer contain organic matter, the nitrogen will be 
mixed with aqueous vapor and carbon dioxid. The former is con- 
densed before reaching the azotometer, anrl the latter is absorbed 
by the potassium hydroxid. When the sample is wholly of a min- 
eral nature it should be mixed with some pure sugar, about half 
a gram, before being placed in the tube. When bubbles of gas no 
longer come over, the heat should be carried back until there is 
a gradual evolution of carbon dioxid under the conditions above 
noted. Finally, the gas is turned off and the pump kept in opera- 
tion until the manometer again shows a perfect vacuum, when 



CALCULATION OF RESULTS 



33^ 



the operation may be considered finished. In the manipulation, 
our chief variation from the official method consists in connect- 
ing the combustion apparatus with the measuring tube before the 
heat is applied to the front end of the combustion tube. Any 
particles of the sample which may have stuck to the sides of the 
tube on filling, will thus be subject to combustion and the gases 
produced measured. Where it is certain that no such adhesion 
has taken place, it is somewhat safer on account of the possible 
presence of occluded gases to heat the front end of the tube before 
connecting the combustion apparatus with the azotometer. 

291. Method of Johnson and Jenkins. — In the method of 
Johnson and Jenkins the principal variation from the process 
described consists in introducing into the combustion tube a 
source of oxygen whereby any difficultly combustible carbon may 
be easily oxidized and all the nitrogen be more certainly set free."** 
The potassium chlorate used for this purpose is i)laced in the 
posterior part of the tube, which is bent at a slight angle 
to receive it. The sodium bicarbonate is placed in the anterior 
end of the tube. The combustion goes on as already descrii)e(l, 
and at its close the potassium chlorate is heated to evolve the 
oxygen. The free oxygen is absorbed by the reduced copper 
oxid, or consumed by the unburned carbon. Any excess of 
oxygen is recognized at once by its action on the copper spiral. ' 
As soon as this shows signs of oxidation the evolution of the gas 
is stopped. Care must be taken not to allow the oxygen to come 
off so rapidly as to escape entire absorption by the contents of 
the combustion tube. In such a case the nitrogen in the meas- 
uring tube would be contaminated. 

It is rarely necessary in fertilizer analysis to have need of more 
oxygen than is contained in the copper oxid powder in contact 
with the sample during the progress of combustion. 

292. Calculation of Results.— The nitrogen originally present 
in a definite weight of any substance having been obtained 
in a gaseous form, its volume is read directly in the burette in 
which it is collected. This instrument may be of manv forms 
but the essential feature of its construction is that it should be 
** American Clietnical Journal, i88o-Sr, 2 : 27. 



I 
I 

- L " 

t 



-^ 



ZZ2 



AGRICULTURAL, ANALYSIS 



READING the: barometer 



Z^^ 



f 



accurately calibrated, and the divisions so graduated as to per- 
mit of the readinp^ of the volume accurately to a tenth of a cubic 
centimeter. For this purpose it is best that the internal diame- 
ter of the measuring tube be rather small so that at least each 
lo cubic centimeters occupies a space lo centimeters long. 
The volume occupied by any gas varies directly with the tem- 
perature and inversely with the ])ressure to which it is subjected. 
The (juantity of aqueous vajKjr which a moist gas may contain 
is also a factor to be considered. Inasnuich as the nitrogen in 
the above process of analysis is collected over a strong solution 
of potassium hydroxid capable of practically keeping the gas in 
a dry state, the tension of the aqueous vapor may be neglected. 

293. Eeading- the Barometer. — Nearly all of the barometers in 
use in this country have the scale divided in inches and the 
thermometers thereunto attached are graduated in Fahrenheit 
degrees. This is especially true of the barometers of the Weather 
Bureau, which are the most reliable atul most easy of access to 
analysts. It is not necessary to correct the reading of the 
barometer for altitude, but it is important to take account of the 
temperature at the time of observation. There is not space here 
to give minute directions for using a barometer. Such direc- 
, tions have been prej^ared by the Weather Bureau and those 
desiring it can get copies of the circular.^^ 

The temperature of a barometer afifects its accuracy in two 
ways: First, the metal scale expands and contracts with chang- 
ing temperatures; Second, the mercury expands and contracts 
also at a nuich greater rate than the scale. If a barometer tube 
holds 30 cubic inches of mercury, the contents will be one 
ounce lighter at 80° F. than at 32° F. The true pressure of the 
air is, therefore, not shown by the observed height of the mercurial 
column, unless the temperature of the scale and of the mercurial 
column be considered. 

Tables of correction for temperature are computed by simple 
formulas based on the known coefficients of expansion of mer- 

^^ Barometers and the Measurenieiit of Atmospheric Pressure, 2ii(l Kdi- 
tion, 1901. 



t i 



a 



cury and brass. For barometers witli brass scales the following 
formula is used for making- the correction : 

'..'3' + .'^s • ^" *•''« formula, / =:= temperature in 

degrees Fahrenheit and /,=observed reading of the barometer 
in inches. 

£.n;«;/'/i?:— Temperature observed y2\^ 

Barometer reading observed, 29.415 inches, 
from which C=o.ii65, and this number, according to the con- 
ditions of the formula, is to be subtracted from the observed 
readmg. The true reading in the case given is, therefore, 
29.298 inches or 744.2 millimeters. 

The observed reading 747.1 
And the correction 2.9 

Unless extremely accurate work be require.!, the correction for 
temperature is of very little importance in nitrogen .Ictermina- 
tions m fertilizers. Each instrument sent out bv the Weather 
Bureau is accompanied by a special card of corrections therefor 
but these are of small importance in fertilizer work In order 
then to get the correct weight of the gas from its volume, the 
reading of the thermometer and barometer at the time of meas- 
urement must be carefully noted. However, after the end of the 
combustion, the azotometer should be carried into another 
room which has not been affected by the combustion an<l allowed 
to stand until it has reached the room temperature. 

Every true gas changes its volume under var\ing tempera- 
tures at the same rate, and this rate is the coefficient of gaseous 
expansion. 1- or one degree of temperature it amounts to 0.003665 
of Its volume. Representing the coefficient of expansion by K 
the volume of the gas as read by V, the volume desired at 'any 
temperature by V, the temperature at which the volume is read 
by / and the desired temperature by t', the change in volume 
may be calculated by the following formula: 

V'=Vfi-fK(/'— /)]. 
Example— l^et the volume of nitrogen obtained bv combus- 
tion be 35 cubic centimeters, an.l the temperature of observa- 
tion 22°. What would be the volume of the gas at 0° ? 



KM 






«s* 



334 



AGRICULTURAL ANALYSIS 



TENSION OF AQUEOUS VAPOR 



335 



' t 



Making the proper substitutions in the formula the equation 
is reduced to the form below : 

V'=:35 1 1 +0.003665 (o°— 22° ) ] 
or V'=35( 1-0.08063)^=32.18. 

Thirty-five cubic centimeters of nitrogen, therefore, measured 
at 22° becomes 32.18 cubic centimeters when measured at o*^. 

When gases are to be converted into weight, after having been 
determined by volume, their volume at 0° must first be deter- 
mined ; but this volume must also be calculated to some definite 
barometric pressure. By common consent, this pressure has been 
taken as that exerted by a column of mercury 760 millimeters in 
height. Since the volume of a gas is inversely proportional to 
the pressure to which it is subjected, the calculation is made 
according to that simple formula. Let the reading of the barom- 
eter, at the time of taking the volume of gas, be H, and any other 
pressure desired H'. Then we have the general formula : 

HV 



V:V' =: H':H; and V = 



H' 



Example : Let the corrected reading of the barometer at the 
time of noting the volume of the gas be 740 millimeters, and the 
volume of the gas reduced to 0° be 32.18 cubic centimeters. 
What will this volume be at a pressure of 760 millimeters? 

Substituting the proper values in the formula, we have : 



V 



32.18 X 740 
760 



= 31.33. 



Therefore, a volume of nitrogen which occupies a space of 
35 cubic centimeters at a temperature of 22°, and at a baro- 
metric pressure of 740 millimeters, becomes 31.33 cubic centime- 
ters at a temperature of 0° and a pressure of 760 millimeters. 

One liter of nitrogen at 0° and 760 millimeters pressure weighs 
Jf-2545^ grams; and one cubic centimeter, therefore, 0.00125456 
gram. To find the weight of gas obtained in the above supposed 
analysis, it will only be necessary to multiply this number by 
the volume of nitrogen expressed in cubic centimeters under the 
standard conditions; viz., 0.0125456X31.33=0.039305 gram. 



If the sample taken for analysis weighed half a gram, the per- 
centage of nitrogen found would be 7.85. 

294. Tension of the Aqueous Vapor.— It has been shown by 
experience that when a gas is collected over a potash solution 
containing 50 per cent, of potassium hydroxid, the tension of 
the aqueous vapor is so far diminished as to be of no perceptible 
influence on the final result. To correct the volume of a gas 
for this slight tension would involve an unnecessarv calculation 
for practical purposes. If a gas thus collected should be trans- 
ferred to a burette over mercury, on which some water floats, 
then the correction should be made. 

At 0° the tension of aqueous vapor will support a column of 
mercury 4.525 millimeters, and at 40^ one 54.969 millimeters 
high. 

The following table gives the tension of aqueous vapors in mil- 
limeters of a mercurial column for each degre-^ of temperatuie 
from zero to 40. 



Temperature. 


Tension of vapor 
in millimeters. 


Temperature. 


Tension of vapor 
inminimeters. 


0° 


4.525 


21° 


18.505 


1° 


4.867 


22° 


19.675 


2° 


5.231 


23° 


20.909 


3° 


5.619 


24° 


22.211 


4° 


6.032 


25° 


23.582 


5° 


6.471 


26° 


25.026 


6° 


6.939 


27° 


26.547 


/ 


7.436 


28° 


28.148 


8° 


7.964 


29° 


29.832 


9° 


8.525 


30° 


31.602 


10° 


9.126 


31° 


33.464 


11° 


9751 


32° 


35.419 


12* 

. _ 


10.421 


33° 


37-473 


13 


II. 130 


34* 


39.630 


14** 


11.882 


35° 


41.893 


15° 


12.677 


36° 


44.268 


16° 


J3.519 


37° 


46.758 


17° 


14.409 


38° 


49.368 


18° 




15.351 


39° 


52.103 


19° 


16.345 


40° 


54.969 


20° 


17.396 







When a gas is in contact with 
fused throughout the mass, and 



water the aqueous vapor is dif- 
the pressure to which the mix- 



n¥ 



"> 



33^ 



AGRICULTURAI, ANALYSIS 



TABLES FOR CALCULATING RESULTS 



2>Z7 



!? 
\\' 

V 
rj 

\-h 



\% 



ture is subjected, is partly neutralized by the tension of the water 
vapor. The real pressure to which the gas, whose volume is to 
be determined, is subjected is, therefore, diminished by that ten- 
sion. If, for instance, a gas in contact with v/ater show a vol- 
ume of 35 cubic centimeters at 22° and 740 millimeters baromet- 
ric pressure, its volume is really greater than if it were perfectlv 
dry. How much greater can be determined by inspecting the 
table; for at 22° the tension of water vapor is 19.675 miUime- 
ters of mercury. The real pressure to which the volume of gas 
is subjected is, therefore, 740 — 19.675=1:720.325 millimeters. 

If, therefore, in the example given, the nitrogen w^ere in con- 
tact with water, the calculation would proceed as follows: 

32.18 X 720.325 



V =^ 



And 30-5 X 1.25456=38.26. 



760 



30-5. 



Millimeters tension of aqueous vapor for KOH solutions of 



Tempera- 
ture. 
10°. 00 

11°. 00 

12°. 10 

13°. 00 

13°. 95 

I5°.i5 

16°. 00 

17°. CK) 
18°. 00 
19°. 00 

20°. CX) 

21°. 00 
21°. 82 
23°. 00 
24°. 00 
25°. 00 
26°. 00 
26°. 98 

27°-93 
29°. 00 

30°. 00 

31°. CX) 

32°. 13 

33°-oo 
34° .00 



9.09 per 
cent. 
8.62 

9.21 

9.90 

10.50 

II. 17 

12.06 

12.74 

13-57 
14.46 

' 15.39 
16.38 
17.42 
18.32 
19.68 
20.92 
22.19 

23.55 

24.95 
26.38 

28.08 

29.76 

31.51 
33.61 

35.30 
37.34 



16.66 per 
cent. 
8.01 

8.56 
9.21 

9-77 
10.39 

11.22 

11.85 
12.63 

13.45 
14.33 
15.25 
16.22 
17.06 
18.32 

1947 
20.67 

21.94 
23. 25 

24.59 
26.18 

27.74 
29.38 

31.34 
32.93 
34.84 



23.08 per 
cent. 

7.31 
7.82 

8.41 

8.92 

9-49 
10.25 

10.82 

11.54 
12.29 

13.09 

13.93 

14.82 

15.59 

16.75 

17.80 

18.91 
20.07 
21.27 
22.51 
23.96 
25.40 
26.91 
28.72 
30.18 

31.94 



28.57 per 
cent. 
6.50 

6.95 
7.47 
7.93 
8.44 
9.II 
9.62 
[O.26 

to.93 
1.65 
2.40 
3.20 

13.88 

4.92 
5.86 
6.85 

7.89 
[8.96 

20.07 
21.38 
22.67 
24.03 

25.65 
26.97 
28.56 



32.89 per 
cent. 
5.62 

6.01 

6.46 

6.86 

7.30 
7.86 

8.33 
8.88 

9-47 
10.09 

10.75 

11.44 

12.04 

12.94 

13.76 
14.62 

15.53 
16.46 

17.45 

18.59 
19.72 

20.91 

22.34 

23.50 
24.89 



Hence, 38.26 milligrams of nitrogen correspond to 7.65 per 
cent., when half a gram of substance is taken for the combustion. 

295. Aqueous Tension in Solutions of Potassium Hydroxid.— 
Even in strong solutions of potassium hvdroxid the tension of 
aqueous vapor is not destroyed, but is reduced to a nn-nimum, 
which is negligible in the calculation of the percentage by weight 
of the nitrogen in a sample of fertilizer. When (Hiute solutions 
of a caustic alkali are used, however, the neglect of the tension of 
the aqueous vapor may cause an error of some magnitude. In 
such cases the strength of the solution should be known and cor- 
rection made according to the preceding table."" 

296. Use of Volumetric Method.— For practical purposes it 
may be said, that the volumetric determination of nitrogen in 
lertilizer analysis has gone entirely out of use. For control and 
comparison it is still occasionally practiced, but it has had to give 
way to the more speedy and fully as accurate processes of moist 
combustion with sulfuric acid, which have come into general use 
in the last two decades. The student and analyst, however, should 
not fail to master its details and become skilled in its use. There 
are certain nitrogenous substances, such as the alkaloids, which are 
quite refractory when subjected to moist combustion. While 
such bodies may not occur in fertilizers, except in rare ca.ses 
such as nicotine in tobacco waste, it is well to have at hand 
a means of accurately determining their nitrogen content. 

297. Tables for Calculating Results.— Where many analy- 
ses are to be made by the copper oxid process, it has proved con- 
venient to shorten the work of calculating analyses by taking 
the data given in computation tables.^' Before using the.se 
tables it must be known whether they are calculated on the sup- 
position that the gas is measured in a moist state, partlv moist, or 
wholly dry. Where the nitrogen is collected over water, a table 
must be used in which allowance has been made for the tension 
of aqueous vapor. In case a saturated solution of a caustic 
alkali be used in the azotometer, it is customary to take no 
account of the tension and the table employed must be con- 

tion.^str -^68 ^"'^ ^«^"s^^i"' Physikalisch-cheniische Tabellen, 2nd Edi- 
«^ Battle and Dancy, Conversion Tables, 1885 : 34. 



.'?# 



<;f 



"If. v 



338 



AGRICULTURAL ANALYSIS 






1 t^^ 



structed on this supposition. In point of fact even in the strong- 
est alkah sohition there is a certain amount of tension but this 
is so sHght as only to affect the results in the second place of 
decimals. Since, as a rule, only a few analyses are made by this 
method, it will be found safer to use a caustic alkali solution of 
given strength and to calculate the results from the tables of 
aqueous tensions given above. 

2q8. The Soda-Lime Process. — This process originally per- 
fected by Varrentrap and Will, and improved by Peligot, was 
used very extensively by analysts until within the last two decades 
for the determination of nitrogen not existing in the nitric form. 
It is based on the principle that when nitrogen exists as a salt 
of ammonia, or as an amid, or as i)roteid matter, it is con- 
verted into gaseous ammonia by combustion with an alkali. 
This ammonia can be carried into a set solution of acid by a stream 
of gas free of ammonia and the excess of acid remaining after 
the combustion is complete can be determined by titration against 
a standard alkali solution. The results under proper conditions 
are accurate even when a small quantity of nitric nitrogen is 
present. When, however, there is any considerable quantity of 
this compound in the sample the method becomes inapplicable 
by reason of non-reduction of some of the nitrogen oxids pro- 
duced by the combustion. 

ill bodies very rich in nitrogen, such as urea, all the nitrogen 
is not transferred directly into ammonia at the commencement 
of the combustion. A portion of it may unite with a part of the 
carlx)n to form cyanogen, which mav unite with the soda to 
form sodium cyanid. Witli an excess of alkali, however, and 
prolonged combustion, this product will be finally decomposed 
and all the nitrogen be secured as ammonia. 

The nascent hydrogen which unites with the nascent nitrogen 
during the combustion is also derived from the organic matter 
which always contains enough carbon to decompose the water 
formed in order to be oxidized to carbon dioxirl. \Miile at first, 
therefore, during combustion, the hydrogen may unite with the 
oxygen, it becomes again free by the oxidation of the carbon and 
u\ this condition unites with the nascent nitrogen to form ammo- 



v« 



THE OFFICIAL METHOD 



339 



nia. In addition to carbon dioxid, ammonia, and free hydrogen 
there may also be found among the products of combustion 
marsh and olefiant gases and other hydrocarbon compinmds 
which dilute, to a greater or less extent, the ammonia formed 
and help to carry it out of the combustion tube and into the 
standard acid. 

299. The Official Method.— Reagents and Apparatus. (i) 

Standard solutions and indicator the same as for the kjeldahl 
method. 

(2) Dry granulated soda-lime, fine enough to pass a 2.5 milli- 
meter sieve. 

(3) Soda-lime, fine enough to pass a 1.25 millimeter sieve. 
Soda-lime may be easily and cheaply prepared by slaking two 

and one-half parts of quicklime with a strong solution of one part 
of commercial caustic soda, care being taken that there is enough 
water in the solution to slake the lime. The mixture is then 
dried and heated in an iron pot to incipient fusion, and, when 
cold, ground and sifted as above. 

(4) Sodium Carbonate and Lime or Slaked Lime. — Instead of 
soda-lime Johnson's mixture of sodium and calcium carbonate, 
or slaked lime, may be used. Slaked lime may be granulated by 
mixing it with a little water to form a thick mass, which is dried 
in the water-oven until hard and brittle. It is then ground and 
sifted as above. Slaked lime is much easier to work with than 
soda-lime, and gives excellent results, though it is probable that 
more of it should be used in proportion to the substance to be 
analyzed than is the case with soda-lime. 

(5) Asbestos. — The asbestos used should be ignited and kept in 
a glass-stoppered bottle. 

(6) Combustion Tubes. — These are about 40 centimeters long 
and with an internal diameter of 12 millimeters, drawn out to 
a closed point at one end. 

(7) ^-T?<^^J.— Large-bulbed U-tubes with glass stop-cock, or 
Will's tubes with four bulbs. 

Manipulation.— The substance to be analyzed should be pow- 
dered finely enough to pass through a sieve of one millimeter 
mesh; from 0.7 to 1.4 gram, according to the amount of nitrogen 



— 1"- inm iB i i 



340 



AGRICULTURAI, ANALYSIS 



the: hydrogkn MKTHOD 



341 






i 



p 
h 



present, is used for the determination. Into the closed end of 
the combustion tube put a small loose plug of asbestos, and upon 
it to the depth of about four centimeters, fine soda-lime. In a 
porcelain dish or mortar mix the substance to be analyzed, thor- 
oughly but (|uickly, with enough fine soda-lime to fill approxi- 
mately 16 centimeters of the tube, or about 40 times as much soda- 
lime as substance, and put the mixture into the combustion tube 
as: quickly as possible by means of a wide-necked funnel, rinsing 
out the dish and funnel with a little more fine soda-lime, which 
is to be put in on top of the mixture. Kill the rest of the tube to 
within about five centimeters of the end with granulated soda- 
lime, making it as compact as possible by tap{)ing the tube gently 
while held in a nearly upright position during the filling. The 
layer of granulated soda-lime should not be less than 12 centi- 
meters dee]). Lastly, put in a plug of asbestos about two centi- 
meters long, pressed rather tightly, and wipe out the end of the 
tube to free it from adhering particles. 

Connect the tube by means of a well-fitting rubber stopper or 
cork with the U-tube or Will's bulbs, containing 10 cubic centi- 
meters of standard acid, and adjust it in the combustion furnace 
so that the end of the tube j)rojects about four centimeters from 
the furnace suital)ly supporting the U-tube or Will's bulb. Heat 
the portion of the tube containing the granulated soda-hme to a 
moderate redness, and when this is attained extend the heat grad- 
ually through the portion containing the substance, so as to keep 
up a moderate and regular fiow of gases through the bulbs, main- 
taining the heat of the first part until the whole tube is heated 
uniformly to the same degree. Continue the combustion until 
gases have ceased bubbhng through the acid in the bulbs, and 
the mixture of substance and soda-lime has become white, or 
nearly so, which shows that the combustion is finished. The 
combustion should occupy about three-c|uarters of an hour, or not 
more than one h(jur. iixtinguish the i)urners and when the tube 
has cooled below redness break oft the closed tip and aspirate air 
slowly through the ap])aratus for two or three minutes to bring 
all the ammonia into the acid. Disconnect the tube, wash the 
acid into a beaker or flask, and titrate with the standard alkali. 



During the combustion the end of the lube projecting fnmi 
the furnace must be kept heated sufficiently to prevent the con- 
densation of moisture, yet not enough to char the stopper. 11ie 
heat may be regulated by a shield of tin slipped over the pro- 
jecting end of the combustion tube. 

It is found very advantageous to attach a bimsen valve to the 
exit tube, allowing the evolved gases to pass out freelv, but pre- 
venting a violent sucking back in case of a sudden condensation 
of steam in the bulbs. 

300. The Official French Method.— The h>ench chemists pre- 
fer to drive out the traces of ammonia remaining in the com- 
bustion tube by means of the gases arising from the decomposi- 
tion of oxalic acid.«« The operation is conducted bv mixing 
about one gram of oxalic acid with enough of dry granular soda- 
hme to form a layer of four centimeters in length at the bottom 
of the tube. The rest of the tube is then charged substantiallv 
as directed above. At the end of the combustion, the oxalic acid 
is decomposed by heat, furnishing sufficient hydrogen to remove 
from the tube all traces of ammonia which it may contain. The 
French chemists employ for titration, either normal acids and 
alkalies or some decimal thereof, or else an acid of such strength 
as to have each cubic centimeter thereof correspond to 10 milli- 
grams of nitrogen, thus making the computation of results ex- 
ceedingly simple. Such an acid is secured when one liter thereof 
contains 35 grams of pure monohydric sulfuric acid or 45 grams 
of pure crystallized oxalic acid. The corresponding alkaline re- 
agent should contain, in each liter, 40 grams of pure i)otassium 
liydroxid. 

301. The Hydrogen Method.— Thiljaiiit and Warner recoiti- 
nicMKl that the combustion with soda-Hnic be conchictcd in an at- 
mosphere of Iiydrof,a-n; and Loges replaces this by common 
illununatmff gas freed from ammonia l)y conducting it through 

a tube filled with glass balls moistened with dilute sulfuric 
acid''""". 

In these cases the combustion tul>c is left open at both ends 

1897!*^""?""' ^'''''^ <!' Analyse des Mati£-res agricoles. jme Edition, 

"» Zeitsclirift fiir aiialytische Cheniie, 1884, 23 • SS7 
»« Cheiniker-Zeitung, 1884, 8 : 649, 1741. ' ^'' 



342 



AGRICULTURAL ANALYSIS 



OFFICIAL RUFFLE METHOD 



343 



1*1 



i 



r 



and llic materials under the tube confined to the proper posi- 
tion by asbestos phi^s. The gases used act in a merely mechan- 
ical manner and their use afifords so few advantages over the 
method of aspirating air at the end of the conjbustion as to ren- 
der it unadvisable. 

302. Coloration of the Product. — It often happens, especially 
in the combustion of animal products, such as tankage and fish 
scrap, that the acid receiving the ammonia is deeply colored by 
the condensation of some of the other products of combustion, 
'i'his coloration interferes, in a very serious way, with the delicacy 
of the indicator used to determine the end of the reaction. In 
this case the licjuid may be mixed with an alkali and distilled, and 
the ammonia secured in a fresh portion of the standard acid as 
in tlie moist combustion process to be hereafter described. 

303. General Considerations. — (i) Preparation of the Sample. 
— In the soda-lime method it is of great importance that the 
organic substances be in a fine state of subdivision so as to ad- 
mit of intimate mixture with the alkali. In cases where frag- 
ments of hoof, horn, hair, or similar substances are to be pre- 
pared for combustion, it is advisable to first decompose them by 
lieating with a small quantity of sulfuric acid. The excess of 
acid may be neutralized with marble dust and the resulting mix- 
ture dried, rubbed to a fine powder, and mixed with the soda- 
lime in the usual wav. Care must be taken not to lose anv of 
the ammonia from the sulfate, which may possibly be formed in 
mixinti: with the soda-lime in filling the tube. 

(2) J'lirity of Soda-Ume. — The soda-lime employed must be 
entirely free of m'trogenous compounds, and blank combustions 
should be made to establish its purity or to determine the mag- 
nitude of the corrections to be made. 

(3) Temperature.— The temperature of the combustion should 
not be allowed to exceed low redness. At very high tempera- 
tures there would be danger of decomposing the ammonia. 

(4) Aspiration of Air. — before aspiring a current of air 
through the tube to remove the last traces of ammonia, the gas 
should be put out under the furnace and the tube be allowed to 



cool below redness to avoid any danger of acting on the nitrogen 
in the air. 

304. The Ruffle Soda-Lime Method. — Many attempts have 
been made to adapt the soda-lime method to the determination of 
nitric nitrogen. Of these, the process devised by Ruffle is the only 
one which has proved successful.^^ The method is founded on 
the action of sulfurous vapors on the nitrogen oxids produced dur- 
ing the combustion, whereby sulfuric acid is formed and the 
nascent nitrogen is joined with hydrogen to form ammonia. By 
this process all the nitrogen contained in the sami)le, even if in 
the nitric form, is finally obtained as ammonia. In the original 
method the reagents employed were sodium thiosulfate, soda- 
lime, charcoal, sulfur, and granulated soda-lime. Subsequently, 
the official chemists substituted sugar for the charcoal. °- The 
method was used for a long time by the official chemists and 
came into general favor until displaced by the simpler and 
cheaper processes of the moist combustion method adapted to 
nitric nitrogen. As finally modified and used by the official chem- 
ists, the process is conducted as described below."^ 

305. The Official Ruffle W^iYio^.—Reao^ents and Apparatus. 
— (i) The standard solutions and indicator arc the same as in 
the kjeldahl method. 

(2) A mixture of equal parts by weight of fine-slaked lime 
and finely powdered sodium thiosulfate dried at 100°. 

(3) A mixture of equal parts by weight of finely powdered 
granulated sugar and flowers of sulfur. 

(4) Granulated soda-lime, as described under the soda-lime 
method. 

(5) Combustion tubes of hard Bohemian glass 70 centimeters 
long and 1.3 centimeters in diameter. 

(6) lUilbed U-tubcs or Will's bulbs, as described under the 
soda-lime method. 

Manipulation.— (2l) Clean the U-tubc and introduce 10 cubic 
centimeters of standard acid. 

(b) Fill the tube as follows: (i) A loosely fitting plug of as- 
«' Journal of the Chemical Society, i88r, 39 : 87. 
^' Division of Chemistry, Bulletin 16, 1887 : 51. 
^ Division of Chemistry, Bulletin 46, Revised Edition, 1899 : 19. 



344 



AGRICULTURAI. ANALYSIS 



h 



lij 

u^ 



bestos, which has been recently ip^nited, is placed in the end of the 
tube to be attaclied to the absorption apparatus, and then 2.5 
lo 3.5 centimeters in depth of the thiosulfate mixture is added. 
(2) The portion of the substance to be analyzed is intimately 
mixed with from five to 10 grams of the sugar and sulfur mix- 
ture. (3) Pour on a piece of glazed pai)er or in a porcelain 
mortar a sufficient (luautity of thiosulfate mixture to fill a depth of 
about 25 centimeters of the tube, add the substance to be analyzed, 
as previously prepared, mix carefully, and pour into the tube, 
shake down the contents of the tube, clean the paper or mortar 
with a small quantity of the thiosulfate mixture and pour into 
the tube, and fill up with soda-lime to within five centimeters of 
the end of the tube. (4) J lace another plug of ignited asbestos 
at the end of the tube and close with a cork. (5) Hold the tube 
in a horizontal position and tap on the table until there is a gas- 
channel along the top of the tube. (6) Make connection with 
the U-tube containing the acid, aspirate and see that the apparatus 
is tight. 

The Combiistiou.—rhcQ the prepared combustion tube in the 
furnace, letting the ends project, so as not to burn the corks. 
Commence by heating the soda-lime portion until it is brought 
to a full red heat. Then turn on slowly jet after jet toward the 
outer end of the tube, so that the bubbles come off at the rate of 
two or three a second, \\1ien the whole tube is red hot and the 
evolution of the gas has ceased and the liquid in the U-tube 
begins to recede toward the furnace, attach the aspirator to the 
other limb of the U-tube. break off the end of the tube, and draw 
a current of air through for a few minutes. Detach the U-tube 
and wash the contents into a beaker or porcelain dish; add a 
few drops of the cochineal solution, and titrate. 

306 Observations.— In our experience we have found it 
much more satisfactory to adhere to the earlier directions for 
preparing the mixture of thiosulfate and alkali. Wr nuich pre- 
fer to make the mixture with soda-lime and without the pre- 
vious drying of the sodium salt. Ruttle himself says that the 
sochum thiosulfate should be dry, but not deprived of its water of 



boyer's modification of ruffle's method 



345 



cry.stallization.'*^ The best method to dry the salt without de- 
priving it of its crystal water is to press it between blotting papers. 
As is seen from the above descri])tion the method is essen- 
tially a reduction process by the action of a powerful deoxidizer 
in the presence of an alkali. The crystals of the thiosulfate salt 
cannot be brought into direct contact with a pure alkali, like soda 
or potash, without forming at once a wet mass which would tend 
to cake and obstruct the tube. The soda-lime is, therefore, a me- 
chanical device to prevent this fusion. Where many analyses 
are to be made, an iron tube, for economical reasons, may be sub- 
stituted for the glass ; but the glass tube permits a more intelli- 
gent observation of the progress of the analysis. 

Since charcoal has very high absorbent powers it will be found 
always to contain a little nitrogen which may be in a form to 
generate ammonia during the combustion. The charcoal used 
should, therefore, be previously boiled with caustic soda or potash 
solution, dried, powdered, and preserved in well-stoppered bot- 
tles. Although pure sugar is practically free of nitrogen, even 
when it is used, it is advisable to occasionally make a blank deter- 
mination and thus ascertain the correction to be made for possi- 
ble contamination. 

307. Boyer's Modification of Ruffle's Method.— The prin- 
ciple of the method rests on the observation that if nitrates be 
heated in a combustion tube with calcium oxalate and soda-lime, 
not more than two-thirds of the total nitrogen appear as ammo- 
ma ; but if a certain proportion of sulfur be added the whole of 
the nitrogen is recovered."-^' The process may be divided into 
two steps ; viz. : 

(i) Action of the calcium oxalate upon the sodium nitrate in 
presence of soda-lime. 

(2) The action of sulfurous acid and of calcium oxalate upon 
the sodium nitrate in presence of soda-lime. 

The analysis is conducted as follows : Dry and pulverize one- 
half gram of nitrate and mix it intimately with 50 grams of the 
reducing compound containing approximately 10 per cent, sulfur, 

''* Journal of the vSociety of Chemical Industry, 1883, 2 : 21. 
»^ Comptes rendus, 1891, 113: 503. 



34^ 



AGRICULTURAL ANALYSIS 



! » 



22.5 per cent, neutral calcium oxalate, and 67.5 per cent, soda-lime. 
Tlie combustion tube has a leni^th of 55 centimeters and a diame- 
ter of 17 millimeters, and is charged as follows: 

Two grams pulverized calcium oxalate. 

Ten grams j)ulverized soda-lime. 

Ten grams of the reducing compound. 

The nitrate incorporated w^ith 50 grams of the reducing mix- 
ture : 

Ten grams of the reducing mixture. 

Ten grams pulverized soda-lime. 

The tube is then tightly closed with an asbestos plug and heated 
gradually from the front backwards, the calcium oxalate fur- 
nishing finally the gas necessary to drive out the last traces of 
ammonia. 

The combustion should be terminated in 40 minutes and when 
completed, the acid, containing the ammonia, is placed in a beaker 
and boiled for two or three minutes to drive off the sulfurous 
and carbonic acids. The titration is then conducted in the usual 
manner. 

The combustion can be carried on just as well in an iron tube 
as in a glass one. The reagents employed, especially soda-lime, 
being hygroscopic, a little water is disengaged in heating, which 
is condensed at the cold extremity of the tube, and which may 
absorb a little ammonia unless special precautions are taken to 
have the materials dry. 

The process is etjually applicable to the determination of nitro- 
gen in all its forms or to mixtures thereof. The method has also 
been applied to the mixture of ammoniacal and organic nitrogen 
and to the mixture of ammoniacal, nitric, and organic nitrogen, 
the combustions having been made both in an iron and a glass 
tube. The amounts of material to be used vary from one-half 
gram to a gram, according to its richness in nitrogen. 

THE MOIST COMBUSTION PROCESS 

308. Historical— As long ago as 1868 Wanklyn proposed to 
conduct the combustion of organic bodies in a wet way, using 
potassium permanganate as the oxidizing body.«« About 10 years 

^ Journal of the Chemical Society, 186.S, 21 : 161. 



METHOD OF^ KJKLDAIIL 



347 



after this he- attempted to extend the method so as to estimate 
the quantity of proteid matter in a sample by treatment with an 
alkaline solution in presence of the permanganate salt. One gram 
of the finely pulverized sample was treated in a liter flask with 
one-tenth normal potash lye. According to the supposition of 
Wanklyn, pure albuminoid matters thus treated yielded o.i of 
their weight of ammonia, or about 50 per cent, of the total nitro- 
gen appeared as ammonia. The ainmonia content of the sample 
was determined by the colorimetric process devised by Nessler. 
It is needless to add that the process of Wanklyn proved to be 
of no practical use whatever, acting differently on different al- 
buminoid matters, and even on the same substance. No other 
attempt was made to perfect the moist combustion process until 
Kjeldahl introduced the sulfuric acid method in 1883. The sim- 
plicity, economy, and adaptability of this method have brought it 
into general use. At first the process was only applied to organic 
nitrogenous compounds in the absence of nitrates, but especially 
by the modifications proposed by Asboth, Jodlbauer, and Scovell 
It has been made applicable to all cases, with the possible exception 
of a few alkaloidal and allied bodies. The moist combustion pro- 
cess for determining nitrogen is now generally employed by 
chemists in all countries, not only for fertilizer control, but also 
for general work. 

309. The Method of Kjeldahl.— The process originally pro- 
posed by Kjeldahl is applicable only to nitrogenous bodies free 
of nitric nitrogen. The principle of the process is based on the 
action of concentrated sulfuric acid at the boiling-point in de- 
composing nitrogenous compounds without producing volatile 
combinations and the subsequent completion of the oxidation by 
means of potassium permanganate. The original process has 
been modified by many analysts, but the basic principle of it has 
remained unchanged. It will, therefore, prove useful here to 
describe the process as originally given. ''^ 

The substance is placed in a small digestion flask of resistant 
glass. Liquids which are not decomposed on heating are evap- 
orated in a thin glass dish, which can be ground up and placed 

»' Zeitschrift fiir analytische Chemie, 1883, 22 : 366. 



m 



348 



AGRICULTURAL ANALYSIS 



MKTIIOD OF KJKLDAHL 



349 



1 1 •' 
[i '. 

i! * 

If 

L> ■ 
h ..: 



in the fli^estion flask with the desiccated sample. The strongest 
sulfuric acid is added in sufficient (juantity, not less than lo cubic 
centimeters in any case, to secure complete decomposition. The 
acid must be free of ammonia and be kept in such a way as not 
to absorb ammonia from the atmosphere of the laboratory. To 
guard against danger of error from such an impurity, frequent 
control determinations should be made. In control experiments 
one or two grams of pure sugar are used as the organic matter. 
If the acid employed contain traces of ammonia, the necessary 
corrections should be made in each analysis. 

The flask having been charged is placed on a wire gauze over 
a small flame. The organic matter becomes black and tar-like, 
and soon there is a rapid decomposition, attended with the evolu- 
tion of gaseous products, among which sulfur dioxid is found. 
'Jo avoid danger from spurting, the digestion flask is placed in an 
oblique position. The flask should have a capacity of at least 
lOO cubic centimeters, and a long neck and be made of a kind of 
glass capable of withstanding the action of the boiling acid. Par- 
ticles of the carbonized organic matter left on the sides of the 
flask by the foaming of the mass at first are gradually dissolved 
by the vapors of the boiling acid as the digestion proceeds. The 
action of the sulfuric acid is not entirely finished when gases 
cease to be given off, but the digestion should be continued until 
the li(juid in the flask is clear and colorless, or nearly so. Usually 
about two hours are required to secure this result. When aided 
by the means mentioned below, the time of digestion can be very 
materially shortened. By adding some fuming sulfuric acid, or 
glacial i)hosi)horic acid, the dilution caused by the formation of 
water in the combustion of the organic matter can be avoided. 
For albuminoid bodies it is hardly necessary to continue the 
combustion until all carbonaceous matter is destroyed. The full 
complement of ammonia is usually obtained after an hour's com- 
bustion, even if the lifpu'd be still black or brown, but with other 
nitrogenous bodies the case is different, so that upon the whole 
it is safest to secure complete decoloration. 

The temperature must be maintained at the boiling-point of 



the acid or near thereto, since at a lower temperature, for instance 
trom loo to I50^ the formation of an.monia is incon.plete' 
bmce all organic substances of whatever kind are dissolved by 
the bodmg acid the previous pulverization of the material need 
be earned only far enough to secure a fair sample. Many sub- 
stances give up practically all their nitrogen as ammonium sul- 
fate when heated with sulftiric acid, as, for instance, urea as- 
paragin, and the glutens, in most of the other organic bodies 
iully 90 per cent, of the nitrogen is likewise secured as the am- 
n.onium salt. In the aromatic compounds, or even m the form 
•of amid m andin salts, the nitrogen is more resistant to the action 
of su furic acid. In the alkaloids where the nitrogen is probably 
a real component of the benzol skeleton, the formation of am- 
moma is very incomplete. iUit even in the cases where the con- 
version of the nitrogen into ammonia is practicallv perfect it is 
advisable to finish the process by completing the oxidation' with 
potassium permanganate. The permanganate should be used in 
a dry povvdered form and added little by little to the hot con- 
tents of the digestion flask, the latter being held in an upright 
position and removed meanwhile from the lamp. When carefully 
performed there is no danger of loss of ammonia, although the 

tion of 1" U Vr' " "'^"'""^ '' ^" ^^^ ^^^^-^^d -^^^^ evolu- 
tion of light. 1 he permanganate must always be added in excess 

and until a permanent green color is produced. The flask is 
hen gently heated for from five to 10 minutes over a small flame 
hut his IS not important. The heating must not be too strong' 
or else a strong evolution of oxygen will take place, with a con-' 
sequent reduction of the manganese compound. When this hap- 
,pens the liquid again becomes clear and there is a loss of am- 
monia. 

After cooling, the contents of the flask are diluted with water 
he green color giving place to a brown, with a rise of tempera' 

r?nt n'°?''"^ ^ '''°"^ *"""• '^' ^'^"'^ i^ hrot,ght into a 

d.st,llat.on flask of about three-quarters of a liter capacity and 

attached to a condenser which ends in a vessel containing titrate.! 

sulfuric acd. About 40 cubic centimeters of sodium hydroxid 

^solution of , .3 specific gravity are added and the stopper at once 



> ¥9 



I J. 

m 



H 



350 



AGRICULTURAL ANALYSIS 



inserted .to prevent any loss of ammonia. To prevent bumping, 
some zinc dust is added, securing an evolution of hydrogen diir- 
u)^ the progress of the distillation. In this case the bumi)ing is 
prevented until near the end of the operation, when it begins 
anew, probably by reason of the separation of solid sodium 
sulfate. After the end of the distillation, the excess of acid re- 
maining in the receiver is determined by a set alkali solution, 
and thus the f(uantity of ammonia obtained easily calculated. 
Kjeldahl, however, preferred to titrate the solution after adding 
potassium iodate and iodid, a mixture which in the presence of 
a strong acid sets free a quantity of iodin equivalent to the free 
acid i)resent. The iodin thus set free is titrated by a set solu- 
tion of sodium thiosulfate, using starch as an indicator. The 
merits of this method are sharpness of the end reaction and the 
possibility of using only a small (juantity of the nitrogenous body 
for the combustion. The sulfuric acid used in the receiver is 
made of the same strength as the thiosulfate solution ; viz., about 
one-twentieth normal. Thirty cubic centimeters of this were 
found to be the proper amount for use with substances oxidized 
in such (|uantities as to produce ammonia enough to neutralize 
about half of it. The titration is carried on as follows: A few 
crystals of potassium iodid are dissolved in the acid oiixture ob- 
tained after the distillation is completed, then a few drops of the 
starch-paste, and finally a few drops of a four per cent, solution 
of potassium iodate. The iodin set free is then oxidized by the 
addition of the one-twentieth normal sodium thiosulfate solution, 
until the blue color disappears. 

Example: Sulfuric acid used, 30 cc. 
Equivalent to sodium thiosulfate, 30 cc. 
Blank combustion recjuired, 29.8 cc. thiosulfate solution. 

Combustion of 0.645 gram of bar- 
ley required, 14.5 cc. " '* 
Thiosulfate corresponding to bar- 

^^y» 15.3 cc. 

In the computation it is more simple to multi])ly the corre- 
sponding number of cubic centimeters of thiosulfate by seven, 
half the atomic weight of nitrogen, and divide the product by the; 



METHOD OF KJELDAHL 



351 



weight of the substance, which will give the per cent, of nitro- 
gen therein. 

15-3 X 7 __ 



Then 



647^ — ^'^^ =^ per cent, of nitrogen in sample. 



A more detailed description of the method of making the titra- 
tion follows: After the distillation is finished the condensing- 
tube is rinsed with a little water, after which the sulfuric acid 
unneutralized in the receiver is determined. It is advisable first 
to test the reaction of the distillate with litmus paper before going 
any further; for if at any time all the acid should be found neu- 
tralized it will be necessary to add a sufficient quantity of one- 
twentieth normal sulfuric acid before adding the potassium iodid, 
etc., otherwise the determination will be irreparably lost. Add! 
to the contents of the flask 10 cubic centimeters of the potassium 
iodid and two cubic centimeters of the potassium iodate solutions, 
•described further on, and the sodium thiosulfate is then run in 
from a burette till the fluid, which is constantly kept agitated by 
shaking the flask, shows only a bare trace of vellow coloration 
from the iodin still present. Starch solution is then added, and 
the blue color obtained is at once removed by additional thio- 
sulfate solution. When some experience has been gained, the 
•eye is able to discern, with great certainty, even the slight color- 
ation caused by only a small trace of free iodin. 

In regard to the sensitiveness of the end reaction ntid the ac- 
'curacy of the result, this method of titration leaves nothing to be 
wished for. The strength of the thiosulfate solution is deter- 
nuned in exactly the same manner, and with starch as an indica- 
tor. For this purpose, measure 10 cubic centimeters of one- 
twentieth normal sulfuric acid into an erlenmeyer, add 120 cubic 
•centimeters of ammonia-free water, 10 cubic centimeters of potas- 
sium iodid solution, and two cubic centimeters of iodate solution ; 
add thiosulfate solution till the fluid shows only the above men- 
tioned light yellow tint, then add starch, and finally thiosulfate. 
In this way the strength of the thiosulfate is ascertained, which 
^f course, must be occasiotiaily redetermined, under exactly the 
•same conditions as obtain in the nitrogen determinations, and 



*• i 



V 



35 



2 



AGRICULTCRAI, ANALYSIS 



every possible error is thereby excluded. That the solution once 
decolorized within a short time aj^^iin assumes a deep blue color, 
is a matter of no concern, inasmuch as both solutions are added 
in such a manner that the end reaction lies exactly at the point 
when the starch iodid reaction distinctly disappears. 

310. Theory of the Reactions. — As has been seen above, the 
final product of heating a nitrogenous organic compound with 
sulfuric acid and an oxidizing body is ammonium sulfate. The 
various steps by which this is obtained have been traced by 
Dafert."" 

(ij The sulfuric acid abstracts from the organic matter the 
elements of water. 

(2) The sulfur dioxid produced by the action of the residual 
carbon on sulfuric acid exercises a reducing effect on the nitrog- 
enous bodies present. 

(3) From the nitrogenous bodies produced by the above re- 
duction ammonia is formed by the action of an oxidizing body. 

(4) The ammonia formed is at once fixed by the acid as am- 
monium sulfate. According to the theory of Asboth, the hydro- 
gen which is formed during the action of sulfuric acid on organic 
matter, when in a nascent state, also aids greatly in the produc- 
tion of ammonia. This idea is based on the fact that with those 
bodies which afford a deficit of hydrogen the formation of am- 
monia i^ imperfect.^*" 

311 Preparation of Reagents.— (t) Pure Sulfuric Acid.— As 
is well known, the so-called pure sulfuric acid in the market 
usually contains ammonia, a fact which compelled Kjeldahl to 
determine the (piantity of nitrogen in the acid in every instance, 
and to make correction for the same in the analysis. An acid 
absolutely free from this impurity may, however, readily be pre- 
pared by the distillation of the commercial article in a small glass 
letort holding easily about 400 cubic centimeters. To conduct 
this operation without danger it is only necessary to arrange the 
apparatus so that the heavy fluid is heated to boiling, not from 
the bottom of the retort, but from its sides, and that the upper 

»« Zeitschrift fiir analytische Cliemie, 1885, 24 ; 455. 
^ Chemisches Central-Blatt, 1886 : 165. 






\ 



PREPARATION OF REAGENTS 



353 



portion of the body and neck is kept sufficiently warm to prevent 
the sulfuric acid fumes from condensing and flowing back into 
the retort. Both these ends are attained by surrounding the re- 
tort with a piece of sheet iron, cylinder-shaped beneath, and with 
an oval upper part, having an opening of about one centimeter 
in diameter for the neck of the retort. To conduct the distilla- 
tion, a burner is used with an arrangement for spreading the 
flame. To avoid with certainty all bumping of the sulfuric acid 
and the resulting danger therefrom, the lamp is so arranged that 
only the products of combustion go up between the retort and 
its iron hood, without allowing the flame itself to come into con- 
tact with the glass vessel. The retort should be filled about half 
full, or with 200 cubic centimeters of acid. By this device, with- 
out any danger whatever, about one liter of sulfuric acid may 
be distilled in a day. The retort will stand numerous distilla- 
tions. Once begun, the distillation takes care of itself; it is neces- 
sary to discontinue it when only the bottom of the retort is cov- 
ered witli sulfuric acid, and to fill whh fresh acid through a funnel 
when the retort has cooled off. The first 20 cubic centimeters 
of the distillate going over are collected by themselves and re- 
jected. What comes over later is, as shown by experience, ab- 
solutely ammonia-free, and can be used without any correction 
for the nitrogen determinations according to Kjeldahl. The acid 
is kept in a stoppered bottle in a phce not reached by ammonia 
fumes. The 10 cubic centimeter pipette used for measuring the 
quantity of sulfuric acid required for each determination is fast- 
ened in the perforated rubber stopper with which the bottle is 
kept closed, and is itself closed above by a small rubber tube 
with a plug of glass wool in it. 

(2) Potassium P er man ^(^a}iote. —Cry stah of this salt are crushed 
(not pulverized) with a pestle into small pieces of about one- 
half nn'llimeter size, which are kept in a long glass tube of about 
ten millimeters diameter, closed with a stopper. 

(3) Ammonia-frcc Water. — Common distilled water can not be 
used in the determination of nitrogen according to Kjeldahl, since 
it contains ammonia. Water may be obtained free from ammonia 



;!lf 



rM 



12 



354 



AGRICULTURAL. ANALYSIS 



ti 



II < 



!; 



by redistillation in a larc^c g-lass retort with the addition of a few 
drops of sulfuric acid. All vessels used in the determination 
are rinsed out beforehand with this water. 

(4) Ammonia-frcc Soda-lye is most conveniently prepared by 
addino- 270 grams of common sodium hydroxid in sticks, little 
by little, to one liter of distilled water which is kept continually 
boiling-, by means of a small flame, in a good-sized silver dish. 
The dish is kept covered with a glass plate. Care has to be exer- 
cised not to add the alkali too rapidly, nor in too large quantities 
at a time, for in this case the fluid will boil too violently at every 
addition of the alkali. After the operation is finished the lye is 
at once siphoned into a glass flask, and when cold is poured into 
a glass-stoppered bottle. 

(5) Onc-twcnticth Normal Sulfuric Acid is prepared from sul- 
furic acid and water, both absolutely ammonia-free, and is kept 
in a place where no fumes of ammonia can reach it, in a well- 
stoppered glass bottle, the stopper being smeared with vaseline. 

(6) Sodium TJiiosulfatc Solutiou.— This should be of the same 
strength as the one-twentieth normal sulfuric acid. It is pre- 
pared by dissolving the salt in ammonia-free water and is com- 
pared with the acid, to which has been added potassium iodid 
and iodate, using starch as an indicator, in the manner described 
above. The solution is kept in a well-stoppered bottle, in the 
dark. When the salt and water used are perfectly pure, it will 
keep unchanged for a fong time. 

(7) Potassium Iodid.— Dissolve five grams of chemically pure 
potassium iodid in ammonia-free water and make the volume too 
cubic centimeters. Keep the solution in the dark and in a well- 
stoppered l)ottle. Ten cubic centimeters of this solution are used 
for each determination. 

(S) Potassium Jo date, —Dissolve four grams of chemically pure 
potassium iodate in ammonia- free water and make the volume 
100 cubic centimeters. Use two cubic centimeters of this solu- 
tion for each determination. 

(9:1 Starch Solution.— Digest pure starch for about a week 
with dilute hydrochloric acid, wash perfectly free from chlorin 



MODIFICATIONS OF THE KJELDAllL i'ROCESS 



355 



• 



by decantation, and finally dry it between filter-paper. The starch 
is then suspended in water with the aid of heat. Such a solu- 
tion will keep for an indefinite time if it be saturated with com- 
mon salt. Ten grams of this starch are dissolved in 1,000 cubic 
centimeters of ammonia- free water and one or two cubic centi- 
meters used for each determination. 

312. Modifications of the Kjeldahl Process. — It would he im- 
practicable here to give even a summary of the many unimportant 
changes which the moist combustion process has undergone since 
the first i)ai)ers of its author were published. These changes may 
be divided into three classes ; viz. : 

I. Those changes which refer solely to the quantities of sub- 
stance used for analysis, to the composition of the acid mixture, 
to the duration of the digestion, to the form and size of the flasks, 
both for digestion and distillation, and to the maimer of distilla- 
tion and of titration. For references to the papers on these sub- 
jects th^^ reader may consult Fresenius.' The most important 
of these minor changes are the following : Instead of the titra- 
tion by means of separated iodin most chemists have had recourse 
to the simpler method of direct titration of the excess of acid by a 
set solution of an alkali. Ammonium, barium, sodium, and potas- 
sium hydroxids are the alkaline solutions most employed. This 
process permits of a larger (piantity of the sample being taken for 
combustion and of the use of a larger quantity of acid in the re- 
ceiver. It also implies the use of a larger digestion flask. In fact, 
it is now quite universal to make the digestion in a special glass 
flask large enough to be used also for the distillation. This 
saves one transfer of the material with the possible danger of loss 
attending it. 

In the distillation it is a common practice, especially in Ger- 
many, to do away with the condensing worm and to carry a long 
glass tube from the distilling flask directly into the acid in the 
receiver. The only inconvenience in this method is the heating 
of the contents of the receiving flask, but this is attended with 
no danger of loss of ammonia and the distillate, on account of 
the high temperature it acquires, is left free of carbon dioxid. 
^ Zeitscbrift fiir analytische Cheniie, 1883 to date. 



as^ 



ACRICULTURAI, ANALYSIS 



I 'i 



hi 

i 



i' 



1 



Many of these minor changes have tended to simplify the pro- 
cess, but without affecting the principle of the method in the 
least. 

2. In the second place a class of changes may be mentioned in 
which there is a marked difference in the method of effecting the 
oxidation secured by the introduction of a substance, usually a 
metal, during the digestion for the purpose of accelerating the 
oxidation. In the original process the only aid to oxidation 
was applied at the end of the digestion in the use of potassium 
permanganate. In the modifications now under consideration a 
metallic oxid or metal is applied at the beginning of the diges- 
tion. Copper and mercury are the metals usually employed. A 
separate paragraph will be given to the description of this modi- 
fication known as the process of Wilfarth. 

3. The third class of changes is even more radical in its nature, 
having for its object the adaptation of the moist combustion 
method to oxidized or mineral nitrogen. The chief feature of 
this class of changes consists in the introduction of a substance 
rich in hydrocarbons, and capable of easily forming nitro com- 
pounds, for the purpose of holding the oxids of nitrogen which 
are formed during the combustion and helping finally to reduce 
them to the form of ammonia. The chief varieties of this class 
of changes were proposed by Asboth, Jodlbauer, and Scovell 
and will be fully set forth in separate paragraphs 

313. Method of Wilfarth. ^Tlie basis of this modification as 
already noted rests on the fact that certain metallic oxids have 
the power of carrying oxygen and thus assisting in a catalytic 
way in the combustion of organic matter^ The copper and mer- 
cury oxids are best adapted for this purpose and experience has 
shown that mercuric oxid, or even metallic mercury gives the 
best results. The manipulation is carried out as follows : 

From one to three grams of the sample, according to its rich- 
ness in nitrogen, are heated with a mixture of 20 cubic centimeters 
of acid containing two-fifths fummg and three-fifths ordinary sul- 
furic acid. To this is added about seven-tenths gram of mer- 
curic oxid prepared in the wet way from a mercury salt free of 
' Chemisches Central-Blatt, 1885 : 113. 



KJf:LDAHIv METHOD 



357 



nitrogen. The combustion takes place in the usual kjeldahl 
llask. If the boiling be continued until the liquid is entirely 
colorless, final oxidation with potassium permanganate is unnec- 
essary. To save time the combustion may be stopped when a 
light amber color is reached, and then the oxidation finished with 
permanganate. Before distilling, a sufficient quantity of potas- 
sium sulfid is added to precipitate all the mercury as sulfid and 
thus prevent the formation of mercurammonium compounds 
vyhich would produce a deficit of ammonia. A convenient strength 
of the sulfid solution is obtained by dissolving 40 grams of potas- 
sium sulfid in one liter of water. Bumping at the end of the dis- 
tillation is not usual, especially if potash-lye be used, but should 
it occur it may be stopped by the addition of zinc dust. 

Only when a large excess of potassium sulfid is used is there 
an evolution of hydrogen sulfid, the presence of which, however, 
does not influence the accuracy of the results. 

The presence of mercuric sulfid in the solution tends to pre- 
vent bumping during the distillation, but it is advisable, never- 
theless, to use a little zinc dust. Other minor modifications con- 
sist of preparing the acid mixture with equal volumes of concen- 
trated and fuming sulfuric acid containing in one liter 100 grams 
of phosphoric acid anhydrid, and using metallic mercury instead 
of mercuric oxid^; or a mixture of half a gram of copper sulfate 
and one gram of metallic mercury ; or 0.05 gram of copper oxid 
and five drops of platinic chlorid solution containing 0.04 gram 
of platinum in a cubic centimeter.'* 

314. Kjeldahl Method as Practiced by the Holland Royal Ex- 
periment Station.''— Necessary Reaf^ents: i. Phosphosulfuric 
acid, made by mixing a liter of sulfuric acid of specific gravity 
1.84 with 200 grams of phosphoric anhydrid. 

2. Alkaline sodium sulfid solution, made by dissolving 500 
grams of sodium hydroxid and six grams of sodium sulfid or 
eight and one-half grams of potassium sulfid in a liter of water. 

3. Mercury. 

^ Kulisch, Zeitschrift fiir analytische Chemie, 1886, 25 : 149. 
* Ulsch, Chemisches Central-Blatt, 1886 : 375. 

^ Methoden van Onderzoek aan de Rijkslandbouwproefstations voor het 
Jaar 1894. 



m. 



358 



AGRICU1.TURAI, ANAI^YSIS 



KJELDAIII. METHOD 



359 









11 



I; 



4. Paraffin in small pieces. 

5. Dilute sulfuric acid and dilute potash solution, both of known 
strength. 

6. Pieces of previously ignited pumice stone or of granulated 
zinc. 

7. Neutral solution of rosolic acid or litmus. 
Apparatus.— The necessary apparatus consists of oxidation 

flasks of about 200 cubic centimeters capacity and distillation 
flasks of about 500 cubic centimeters capacity, both of [Bohemian 
glass. Copper may be used for the distillation flasks. 

The Process.— A gram of the sample to be analyzed is placed 
in an oxidation flask, together with 20 cubic centimeters of phos- 
phosulfuric acid and a drop of mercury (about 600 milligrams), 
and heated till the fluid becomes colorless. After cooling, dilute 
and wash the contents of the flask into a distillation flask. The 
resulting volume should be about 300 cubic centimeters. Add 
100 cubic centimeters of the alkaline sodium sulfid solution and 
some pieces of ignited pumice stone or granulated zinc. Distil 
the ammonia, receiving the distillate in a flask containing a known 
volume of the standard sulfuric acid. Titrate with tenth-normal 
potash, using litmus or rosolic acid as indicator. 

315- The Kjeldahl Method as Practiced at the Halle Station. 
—The metlKxl in vogue in the German stations of conducting 
the moist combustion process is well illustrated by the 
method of procedure followed at Halle." From 0.7 to 1.5 
grams of the sample are used for analysis, according to its rich- 
ness in nitrogen. Because of the fact that so small a cpiantity 
of the sample is used, it is of the highest importance that it be 
perfectly homogeiieous throughout its entire mass. Otherwise, 
grave errors may arise. From the sample as sent to the labo- 
ratory the analyst should remove a subsample, and this should be 
rubbed to a fine powder and the part used for analvsis carefully 
selected therefrom. If the sample be moist it may be rubbed up 
with an equal weight of gypsum, in which case a double quantity 
IS employed for the determination. Substances like bone-meal, 
Halle tl^,',892^: ^^"|"^"^*^*^^''"^1' ^'''^ agricultur-chemische VersuchsstatioJ 



|i 



which do not keep well mixed, especially when occasionally 
shaken, should be intimately mixed before each weighing. The 
sample is placed in a glass flask of about 150 cubic centimeters 
capacity. The flask should be made of a special glass to with- 
stand the conditions of the combustion. A globule of mercury 
weighing a little less than one gram is placed in the flask and 
also 20 cubic centimeters of pure sulfuric acid of 1.845 specific 
gravity. The mercury is conveniently measured by an apparatus 
suggested by Wrampelmayer. It consists of an iron tube hold- 
ing mercury, and is conveniently filled, from time to time, from 
a supply vessel placed in a higher position and joined by means 
of a heavy glass tube and rubber tube connections. The lower 
end of the iron tube is provided with a movable iron stopper 
having a pocket just large enough to hold a globule of mercury, 
weighing a little less than a gram. On turning the stopper the 
pocket is brought opposite a discharge orifice and the measured 




Fig. 15. Moist Combustion Apparatus of the Halle Agriculturallvaboratory. 

globule of mercury is discharged. With substances which tend 
to produce a strong foaming a little paraffin is used. The flasks 
after they are charged are placed on circular digesting ovens 
under a hood, as shown in Fig. 15. 

At first the tripodal support of the flasks is so adjusted as to 
bring them between the lamps, and in this way a too rapid re- 
action is at first avoided. After half an hour the tripods are so 
turned as to bring each flask directly over the lamp, the flame 
of which is allowed to impinge directly against the glass. The 
flame is so regulated that after the evolution of the sulfur dioxid 



36o 



AGRICULTURAI, ANALYSIS 



M 



i 



h < . 



has nearly ceased tlio contents of the flask are brought into gentle 
ebullition. The boiling is continued until the contents of the 
flask are colorless, usually about two hours. As a rule such sub- 
stances as cottonseed-meal and dried blood will take a longer 
time for complete combustion than other fertilizing materials 
During the combustion the flasks are closed with an oblong loose- 
fiftiiig unground glass stopper. When the o.xidation is finished 
the contents of the flasks are allowed to cool, the stoppers are re- 
moved, and enough water is added to fill the flasks about three- 
quarters full. The flasks are gently shaken, and the possibility of 
breaking from the heat developed must not be overlooked ' To 
avoid confusion, the flasks are all numbered before beginning the 
work and the numbers noted by the analvst in connection with 
the samples. The contents of each one are ne.xt poured into the 
dis^tillation flask and the digestion vessels are washed with loo 
cubic centimeters of water in three portions and the wash-water 
a.lded to the li,|ui(l. Sometimes in washing out the digestion 
flask yellow basic mercury compounds separate on its walk but 
this does not in any way influence the accuracy of the results 
Ihe (listillatKM, flasks should have about 600 cubic centimeters 

TV\ '^•" "'""''' "'" "■''"'^^'■' ^'^^ digestion may take place in 
the distillation flask, in which case the latter must be made of 
special glass as indicated. 

To the liqui.l thus transferred are a<lde<l 75 cubic centimeters 
ot soda-b^e, containing one and one-half times as "much potas- 
sium ^ulfid as IS necessary to combine with the mercuric sulfate 
present^ 1 he lye is of such a strength that Oo cubic centimeters 
are sufi^c.ent to neutralize the acid present. Tt has a specific 
gravity of ,.375 and contains 33 grams of potassium sulfid in 
a liter. 

JVu'-^° ^^°i'' t'''^ •^"■"Ping vvhich may take place during 
the distillation, some granulated zinc should be arlded 

The distillation flask is closed with a rubber stopper carrying 
a bulb-tube which ends above in a glass tube about three-quar 
ters of a meter long, bent at an acute angle and passing oblimiely 
downwar<l on a convenient support. This tul,e is connected by a 
rubber, with the end tube bent nearly at a right angle and dip- 



, KJI^LDAIIL METHOD 



361 



ping into the standardized acid in the erlenmever receiver. The 
general arrangement of the dislilHiig apparatus is shown in 
Fig. 16. Since the contents of the vessel are warmed by mixing 
with the soda-lye, the flame can be turned on at full head at once 
at the commencement of the operation. In about a quarter of 
an hour the liquid in the receiver will be at the boiling-point, 
and the boiling should be continued for five minutes more, making 
20 minutes in all for the completion of the distillation. By this 
boiling the contents of the receiver are not charged with carbon 
dioxid, as might happen if a condenser were used. The receiver 
contains 20 cubic centimeters of a standardized sulfuric acid solu- 
tion and about 50 cubic centimeters of water. 

The acid used should contain 38.1 grams of sulfuric acid of 
1.845 specific gravity in a liter; and it should be set by titration 







■.,i''iiiiiii..''.iwi!lii| 
Fig. 16. Distillation Apparatus of the Halle Agricultural I^al>oratory. 

With chemically pure sodium carbonate. For this purpose 0.7 
gram of sodium carbonate is heated in a platinum crucible for 
two hours over a small flame, weighed, and placed in an erlen- 
nieyer together with 20 cubic centimeters of the sulfuric acid, 
care being taken to avoid loss from the vigorous evolution of 
carbon dioxid. After boiling for 10 minutes all the carbon dioxid 
is removed from solution. After cooling, the excess of acid is 
determined by titration with a standardized barium hydroxid 
solution, using rosolic acid as indicator. 

The solution of barium hydroxid is made as follows: Digest, 
with warm water, 260 grams of caustic baryta, Ba(OH)2, .until 
It is nearly all dissolved, filter, and make up to a volume of 10 



362 



AGRICULTURAI, ANALYSIS 



liters and keep in a flask free of carbon dioxid. A solution of 
barium hydroxid is to be preferred to the corresponding sodium 
compound for titration. If traces of carbonate be formed in the 
two liquids, the sodium salt will remain in solution while the 
barium compound will settle at the bottom of the flask. 

The Indicator. — The indicator used to determine the end of 
the reaction is made by dissolving one gram of rosolic acid in 
50 cubic centimeters of alcohol. From one to two drops are 
enough for each titration. The color reaction is less definite as 
the quantity of ammonia in the \\i[\.m\ increases. When the titra- 
tion solutions have been prepared as above described it is found 
to re([uirc about 90 of the barium hydroxid to neutralize 20 cubic 
centimeters of the sulfuric acid. 

By direct titration with sodium carbonate it is ascertained how 
many grams of nitrogen the 20 cubic centimeters of sulfuric acid 
represent. 

£.rr7;;//>/r.— Suppose the weight of the dried sodium carbonate 
prepared as above directed is 0.6989 gram. 

i/2Na2C03, 1/2N2 

Then 0.6989 : 53 ~ x : 14 

Whence x=r 0.1846x5 gram of nitrogen. 

Suppose further tliat 20 cubic centimeters of sulfuric acid 
solution require 94 cubic centimeters of barium hydroxid for com- 
plete saturation and after treatment with the above amount of 
sodium carbonate, loj^ cubic centimeters of the bafium solution 
to neutralize the remaining acid. 

Then 94—10.5=83.5 

And 0.184615 : 83.5=x:94. 

Whence x = 0.207830 gram of nitrogen corresponding to 20 
cubic centimeters of the sulfuric acid used. 

Then 0.20783-^94 = 0.002211 gram of nitrogen correspond- 
ing to one cubic centimeter of the barium hydroxid solution. 

If then in the analysis of a fertilizer it is found that 60.5 cubic 
centimeters are required to neutralize the excess of sulfuric acid 
after-distillation, the percentage of nitrogen in the sample is found 
as follows : 



OFFICIAL KJELDAIIL METHOD 



363 



i 



60.5x0.002211=0.13377. 

0.20783 — o. 1 3377^:0.07406. 

0.07406 X 1 00= 7.406= per cent, nitrogen in sample when one 
gram is used for the combustion. 

316. The Official Kjeldahl Method. Not Applicable in the 
Presence of Nitiates. — In order to determine if the sample con- 
tains nitric acid or nitrates, apply the following test:^ 

Mix five grams of the fertilizer with 25 cubic centimeters of 
hot water and filter. To a portion of this solution add two vol- 
umes of concentrated sulfuric acid, free from nitric acid and 
oxids of nitrogen, and allow the mixture to cool. Add cautiously 
a few drops of concentrated solution of ferrous sulfate, so that 
the fluids do not mix. If nitrates are present the junction shows 
at first a purple, afterwards a brown color, or if only a very 
minute quantity be present, a reddish color. To another por- 
tion of the solution add one cubic centimeter of dilute solution of 
nitrate of soda (three grams to 300 cubic centimeters) and test 
as before to determine whether sufficient sulfuric acid was added 
in the first test. 

Preparation of Reagents. — (i) Acids. — (a) Standard hydro- 
chloric acid, the absolute strength of which has been detemiined 
by precipitating with silver nitrate, and w^eighing the silver chlo- 
rid as follows :® 

To any convenient quantity of the acid to be standardized, 
add a solution of silver nitrate in slight excess, and two cubic cen- 
timeters of pure nitric acid, of specific gravity 1.2. Heat to 
boiling-point, and keep at this temperature for some minutes 
without allowing violent ebullition, constantly stirring until 
the precipitate assumes the granular form. Allow to cool 
somewhat, and then filter the fluid through asbestos. Wash 
the precipitate by decantation, with 200 cubic centimeters of very 
hot water, to which have been added eight cubic centimeters 
of nitric acid and two cubic centimeters of dilute solution of silver 
nitrate containing one gram of the salt in too cubic centimeters 
of water. The washing by decantation is performed by adding 

' Division of Chemistry, Bulletin 49, 1897 : 19. 

* Division of Chemistry, Bulletin 46, Revised Edition, 1899 : 14. 



f 



''i 



364 



AGRICULTURAL ANALYSIS 



the hot mixture in small quantities at a time, and beating up the 
precipitate well with a thin glass rod after each addition. The 
pump is kept in action all the time, but to keep out dust during 
the washing, the cover is only removed from the crucible when 
the lluid is to be added. 

Put the vessels containing the precipitate aside, return the wash- 
ings once through the asbestos so as to obtain them quite clear, 
remove them from the receiver, and set aside to recover the excess 
of silver. Rinse the receiver and complete the washing of the pre- 
cipitate with about 200 cubic centimeters of cold water. Half 
of this is used to wash by decantation and the remainder to 
transfer the precipitate to the crucible with the aid of a trimmed 
feather. Finish washing in the crucible, the lumps of silver 
chlorid being broken down with a glass rod. Remove the 
second filtrate from the receiver and pass about 20 cubic centi- 
meters of 98 per cent, alcohol through the precipitate. Dry at 
from 140° to 150^ Exposure for half an hour is found more 
than sufficient, at this temperature, to dry the precipitate thor- 
oughly. It has been proposed to modify this process somewhat 
by directing that the precipitate be washed several times by de- 
cantation instead of with 200 cubic centimeters of water, this 
quantity not being considered sufficient in all cases. 

The alx)ve is the old method of standardizing the hydrochloric 
acid. The method now in use is as follows:" 

By means of a preliminary test with silver-nitrate solution, 
to be measured from a burette, with excess of calcium carbon- 
ate to neutralize free acid and potassium chromate as indicator 
determnie exactly the amount of nitrate required to precipitate 
all the hydrochloric acid. To a measured and also weighed por- 
tion of the standard acid add from a burette one drop more of 
silver-nitrate solution than is required to precipitate the hydro- 
chloric acid. Heat to boiling, cover from the light, and allow 
to stand until the precipitate is granular. Then wash with hot 
water through a gooch crucible, testing the filtrate to prove ex- 
cess of silver nitrate. Dry the silver chlorid at 140° to 150° C. 
(b) Standard sulfuric acid, the absolute strength of which has 
» Bureau of Chemistry, Hulletin 107, 1907 : 5. 



OFFICIAL KJELDAHL METHOD 



365 



been determined by precipitation with barium chlorid and weigh- 
ing the resulting ])arium sulfate : 

For ordinary work half-normal acid is recommended, i. e., 
containing 24.52 grams sulfuric acid to the liter; for determining 
very small amounts of nitrogen, one-tenth normal acid is recom- 
mended. In titrating mineral acids against ammonia solutions, 
use cochineal as indicator. 

(c) Sulfuric acid, specific gravity 1.84, free of nitrates and 
also of ammonium sulfate, whirri is sometimes added in the 
process of manufacture to destroy nitrogen oxids. 

(d) Standard alkali, the strength of which, relative to the 
acid, has been accurately determined. One-tenth normal ammo- 
nia solution, /. .:'., containing 1.7051 grams of ammonia to the 
liter, is recommended for accurate work. 

(e) Metallic mercury or mercuric oxid, prepared in the wet 
way. That prepared from mercuric nitrate can not be safely 
used. 

(/) Potassium permanganate finely pulverized. 

{g) Granidated zinc, pumice stone, or zinc dust (one-half 
gram) is to be added to the contents of the flask during distillation, 
when found necessary, in order to prevent bumping. 

In the laboratory of the Bureau of Chemistry, zinc dust is no 
longer used, since its use tends to break the flask. Pumice stone 
is also no longer used, since experience has shown that granulated 
zinc is best suited to secure the purpose intended. 

{h) Potassium sulHd. — A solution of 40 grams of commercial 
potassium sulfid in one liter of water. 

{i) Soda. — A saturated solution of sodium hydroxid free of 
nitrates. 

(;') Indicator. — A solution of cochineal prepared as follows : 
Digest for a day or two at ordinary temperatures and with fre- 
quent agitation, three grams of pulverized cochineal in a mixture 
of 50 cubic centimeters of strong alcohol with 200 cubic centi- 
meters of distilled water. The filtered solution is employed. 

Apparatus. — (i) Kjeldahl digestion flasks, pear-shaped, round 
bottom, of hard, moderately thick, well-annealed glass: These 
flasks are about 22 centimeters long, having a maximum diame- 



^1 

h1 



u 



y 






366 



AGRICULTURAI, ANALYSIS 



ter Of SIX centimeters and tapering out gradually in a long neck 
wh,ch ,s two centimeters in diameter at the narrowest part, and' 
flared a httle at the edge. The total capacity is about 250 aibic 

centimeters. 

(2) DisUllation iiasks.-For distillation, a flask of ordinary 

is fitL 'h °"' ¥k "•'^'' -"ti-''-^ capacity may be used. It 
•s fitt d w>th a rubber stopper and with a bulb-tube above to pre- 
vent the poss,b.hty of sodium hydroxid being carried over me- 
chanically dunng distillation. The bulbs are about three cent - 
niters in diaineter, the tubes being of the same diameter as the 
ondenser and cut off obliquely at the lower end, which is fastened 
to the tube of the condenser by a rubber tube 

(3) Kjeldahl flanks for both digestion and disfillation.-These 

aTouf^^o h • '■°"."^-'^<^"°- fl--^^' having a total capacity of 
about 550 cubic centimeters, made of hard, moderately thick and 
well-annealed glass. When used for distillation the flasks are 
^^^^witli rubber stoppers and bulb-tubes, as given underl:;! 

Manipulation.-(,) The Disestion.-From seven-tenths to 

l^ee and five-tenths grams of the substance to be analyzed a - 

CO ding to Its proportion of nitrogen, are brought into a d gest on 

flask with approximately seven-tenths gram of mercuric oxTd o^ 

suitur c acid. The flask is placed in an inclined position and 
heated below the boiling-point of the acid for from five 'o^^ 
^.nmes or until frothing has ceased. If the ir.ixturr froths 
badly a small piece of paraffin may be added to p evem i ' 
The heat is then raised until the acid boils briskly. No f ,r h r 
attention is required until the contents of th fl 1 , ^ 

the official methods in place of the spnf«„ k *° 

fiTtlKT attention etc " "p!. T t , " begmnmg "no 

ttention. etc. Boil for at least one hour or until the 



M 



DIGESTION APPARATUS 



367 











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Fig. 18. Distilling Apparatus. 



liquid has become quite clear and nearly colorless. With some 
materials such as leather scrap, cheese, milk, meats, etc., it is 
necessary to digest several hours." 

(2) The Distillation.—Aitcr cooling, the contents of the flask 
are transferred to the distilling flask with about 200 cubic centi- 
meters of water; then a few pieces of granulated zinc, pumice 
stone, or one-half gram of zinc dust when found necessary to 
keep the contents of the flask from bumping, and 25 cubic centi- 
meters of potassium sulfid solution are added, shaking the flask 
to mix its contents. Next add 50 cubic centimeters of the soda 
solution, or sufficient to make the reaction strongly alkaline, 
pouring it down the sides of the flask so that it does not mix at 
once with the acid solution. Connect the flask with the condenser, 
mix the contents by shaking, and distil until all ammonia has 
passed over into the standard acid. The first 150 cubic centi- 
meters of the distillate will generally contain all the ammonia. 
This operation usually requires from 40 minutes to one hour and 
a half. The distillate is then titrated with standard alkali. 

The use of mercuric oxid in this operation greatly shortens 
the time necessary for digestion, which is rarely over an hour 
and a half in case of substances most difficult to oxidize, and is 
more commonly less than an hour. In most cases the use of 
potassium permanganate is quite unnecessary, but it is believed 
that in exceptional cases it is required for complete oxidation, 
and in view of the uncertainty it is always used. The potas- 
sium sulfid removes all the mercury from the solution, and so 
prevents the formation of mercurammonium compounds which 
are not completely decomposed by soda solution. The addition 
of zinc eives rise to an evolution of hvdrogen and prevents vio- 
lent bumping. Previous to use, the reagents should be tested 
by a blank ('X])eriment with sugar, which will i)artially reduce 
any nitrates that are present, which might otherwise escape 
notice. 

317. The Digestion Apparatus Used in the Bureau of Chem- 
istry. — In order t(^ avoid the escape of the fumes of sulfuric acid 
into the working room, the digestions are conducted in a hood 
as illustrated in Fig. 17. The glass doors of the hood are raised 




Fig. 17. Hood. 




Fig. 18. Distilling Apparatus. 



DIGESTION APPARATUS 



367 



liquid has become quite clear and nearly colorless. With some 
materials such as leather scrap, cheese, milk, meats, etc., it is 
necessary to digest several hours." 

(2) The Distillation.—Aitev cooling, the contents of the flask 
are transferred to the distilling flask with about 200 cubic centi- 
meters of water; then a few pieces of granulated zinc, pumice 
stone, or one-half gram of zinc dust when found necessary to 
keep the contents of the flask from bumping, and 25 cubic centi- 
meters of potassium sulfid solution are added, shaking the flask 
to mix its contents. Next add 50 cubic centimeters of the soda 
solution, or sufficient to make the reaction strongly alkaline, 
pouring it down the sides of the flask so that it does not mix at 
once with the acid solution. Connect the flask with the condenser, 
mix the contents by shaking, and distil until all ammonia has 
passed over into the standard acid. The first 150 cubic centi- 
meters of the distillate will generally contain all the ammonia. 
This operation usually requires from 40 minutes to one hour and 
a half. The distillate is then titrated with standard alkali. 

The use of mercuric oxid in this operation greatly shortens 
the time necessary for digestion, which is rarely over an hour 
and a half in case of substances most difficult to oxidize, and is 
more commonly less than an hour. In most cases the use of 
potassium permanganate is quite unnecessary, but it is believed 
that in exceptional cases it is required for complete oxidation, 
and in view of the uncertainty it is always used. The potas- 
sium sulfid removes all the mercury from the solution, and so 
prevents the formation of mercurammonium compounds which 
are not completely decomposed by soda solution. The addition 
of zinc gives rise to an evolution of hydrogen and prevents vio- 
lent bumping. Previous to use, the reagents should be tested 
by a blank experiment with sugar, which will partially reduce 
any nitrates that are present, which might otherwise escape 
notice. 

317. The Digestion Apparatus Used in the Bureau of Chem- 
istry.— Tn order to avoid the escape of the fumes of sulfuric acid 
into the working room, the digestions are conducted in a hood 
as illustrated in Fig. 17. The glass doors of the hood are raised 



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368 



AGRICUI.TURAL ANAI^YSIS 



in order to give a better view of the arrangement of the fur- 
nace. In the furnace there are three sets of eight digestion flasks. 
The neck of each flask is held by an opening into a lead tube of 
five inches diameter, connected with a ventilating flue concealed 
by the tube in the photograph. Any sulfuric acid which con- 
denses in this tube is caught by a vessel placed under the lowest 
part of the lead tube; the volatile products escape in the flue. 

318. The Distillation Apparatus in Use in the Laboratory of 
the Bureau of Chemistry.— -In the nitrogen laboratory of the Bu- 
reau the distilling apparatus is arranged as shown in Fig. 18. The 
flasks are the same as are used in the digestion process. They are 
connected to the block tin condensers by the trap shown in Fig. 19. 
The block tin condensers are contained in an iron tube through 
which cold water flows during the distillation. The trap (Fig. 19) 
above the flask carries an emergent tube which extends to near- 
ly the center of the trap and is bent laterally to avoid any danger 
of carrying over any alkali that may be projected into the trap 
durmg boiling. A small hole near the bottom allows any con- 
densed steam to flow back into the distilling flask. The cold 
water enters the condensers through the pipe provided with a stop- 
cock shown in the center, and leaves bv the two pipes shown at 
the sides of the apparatus. The boiling is continued usually 
for nearly an hour, or until bumping begins. The table on 
vvhich the apparatus is placed is so arranged as to permit of 
easy access on all sides. The standard acid is held in erlen- 
meyers placed on wooden blocks so that the end of the con- 
denser, which is a drawn-out glass tube, dips beneath the surface 
of the acid. 

319. Patrick's Distilling Flask.— To avoid the expense and 
annoyance attending the breaking of the distilling flasks, Patrick 
has proposed to make them of copper.'" The size, about half a 
hter, made for the evolution of oxygen for experimental pur- 
poses, may be used. A little excess of potassium sulfid is used 
tc make up for any of it which might be consumed by the cop- 
per. About 25 cubic centimeters of this solution are recom- 
mended. No zmc or pumice stone is required to prevent bumping, 
'» division of Chemistry, Bulletin 31, 1891 : 742. 



DISTILLATION APPARATUS 



369 




Fig. 19. Trap of Distilling .\pparatus. 



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370 



AGRICULTURAI^ ANALYSIS 



and the distillation may be finished within 30 minutes, thus secur- 
ing a saving of time. There will doubtless be a slight corro- 
sion of the flasks by the sulfid employed, but where the gunning 
oxidation process is practiced this danger would be avoided. 

320. The Gunning Moist Combustion Process. — The modifi- 
cation proposed by Gunning was based upon the observation that 
in the ordinary kjeldahl process the excess of sulfur trioxid in 
the beginning of the operation soon escapes or unites with water 
in a form not easily decomposed." During the progress of the 
combustion the acid diminishes in strength until it is below the 
concentration represented by the formula H2SO4, and in this 
diluted condition the oxidation takes place more slowly. Gun- 
ning proposes to avoid this difficulty by mixing potassium sulfate 
with the sulfuric acid. This salt forms with the sulfuric acid, 
acid salts which, by heating, lose water easier than acid, and, as 
is well known, they not only act as decomposing and oxidizing 
media as well as sulfuric acid, but even in a higher degree, re- 
sembling the action of sulfuric acid at high temperatures and 
under pressure. 

By heating this mixture of sulfuric acid and potassium sulfate 
with organic matters in an open vessel, not only the water origi- 
nally present, but that which is formed during the oxidation, is 
driven off without loss of acid. For this reason instead of the 
oxidizing mixture becoming weaker, the acid becomes stronger, 
the boiling-point rises and this, combined with the fluidity of 
the mass, favors the decomposition and oxidation of the organic 
matter in a constantly increasing ratio. 

The original mixture used by Gunning has the following com- 
position ; viz., one part of potassium sulfate and two parts of 
strong sulfuric acid. The substances are united by heat, and 
on cooling are in a semi-solid state, melting, however, easily on 
the application of heat and assuming a condition that permits 
them to be poured from vessel to vessel. The quantity of the 
sample should vary in proportion to its nitrogenous content from 
half a gram to a gram. The combustion takes place in flasks en- 
tirely similar to those used in the ordinary kjeldahl process. In the 

»i Zeitschrift fiir analytische Chemie, 1889, 28 : 188. 



REACTIONS OF THt GUNNING PROCESS 



371 



case of liquids, they should be previously evaporated to dryness 
before the addition of the oxidizing mixture. At the beginning 
of the combustion there is a violent foaming, attended with evo- 
lution of some acid and much water, and afterwards of stronger 
acid. This loss of acid should not be allowed to go far enough 
to produce too great concentration of the material in the flask. 
One of the best ways to avoid it, is to place a funnel in the 
flask covered with a watch-glass, which will permit of the con- 
densation and return of the escaping acid. As soon as the foam- 
ing ceases, the flame should be so regulated as to permit of the 
volatilized acid being condensed upon the sides of the flask. In 
the end a colorless mass is obtained in which no metallic oxids 
are present, and this mass can at once be diluted with water, 
treated with alkali, and distilled. According to the nature of 
the substance, from half an hour to an hour and a half are re- 
quired for the complete combustion. 

Modifications of the Gunning Method. — As in the case of the 
kjeldahl method, numerous minor modifications of the gunning 
method have been made, the most important of which relate to 
its application to substances containing nitrates. In general the 
same processes are employed in this case as with the kjeldahl 
method. One of the best modifications consists in the use of the 
mixture of salicylic and sulfuric acids, followed by the addition 
of sodium thiosulfate or of potassium sulfate or sulfid. These 
modifications will be given in detail under the official methods. 

321. Reactions of the Gunning Process. — The various reac- 
tions which take place during the combustion according to the 
gunning method have been tabulated by Van Slyke.^'- 

The first reaction to take place is the union of sulfuric acid 
and potassium sulfate to form potassium acid sulfate in accord 
ance with the following equation : 

(i) K,SO,+H,SO,=2KHSO,. 

When heated, the potassium acid sulfate decomposes, forming 
potassium disulfate and water, thus : 

(2) 2KHSO,z::zK2S20, + H.O. 
'^ Division of Chemistry, Bulletin 35, 1892 : 68. 






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AGRICULTURAL ANALYSIS 



The potassium disulfate at a higher temperature decomposes, 
forming normal potassium sulfate and sulfur trioxid, thus: 

(3) K,S,0,=K,S0,+ S03. 
At a sufficiently high temperature the two preceding reactions 
may take place in one, thus : 

2KHSO,=:K2SO,+H20+S03. 

At the temperature at which these reactions take place, the 
water that is set free does not recombine with the sulfur trioxid 
nor with the sulfuric acid that is present in excess, but is ex- 
pelled from the mixture ; hence the mixture becomes more con- 
centrated during the digestion. The sulfur trioxid set free acts 
upon the organic matter in the powerful manner peculiar to it, 
and the potassium sulfate, formed in the last reaction above, unites 
with another molecule of sulfuric acid, and the same round of re- 
actions is repeated continuously so long as there is an excess of 
free sulfuric acid present in the mixture. As the liquid becomes 
more concentrated with the continuation of the digestion, the 
boiling-point increases so that the effect is the same as heating 
under pressure. The danger of too great concentration and risk 
of consequent loss of nitrogen is avoided by using increased pro- 
portions of sulfuric acid. 

As compared with the kjeldahl, the gunning method presents 
the following advantages : 

(i) The gunning method requires fewer reagents. As no form- 
of mercury is used, no potassium sulfid is needed, and there is no 
risk of loss from the presence of mercurammonium compounds. 

(23 The solution to which caustic soda is added is clear, so 
that in neutralizing it is an easy matter to avoid great excess of 
alkali, and so, in most cases, to avoid foaming and bumping in 
distillation. 

(3) In the blank determinations less nitrogen is found in the 
reagents used in the gunning method. In only one case was 
more nitrogen reported in a blank by this method than in the 
other methods ; in all the others the amount was considerably 
less. 

322. The Official Gunning Method.^'^ — In a digestion flask hold- 

^^ Bureau of Chemistry, Bulletin 107, 1907 : 7. 



MODIFICATIONS OF ASBOTH 



373 



ing from 250 to 550 cubic centimeters, place from 0.7 to 3.5 
grams of the substance to be analyzed, according to its propor- 
tion of nitrogen. Add 10 grams of powdered potassium sulfate 
and from 15 to 25 cubic centimeters (ordinarily about 20 cubic 
centimeters) of concentrated sulfuric acid. Conduct the diges- 
tion as in the kjeldahl process, starting with a temperature be- 
low boiling-point and increasing the heat gradtially until all froth- 
ing ceases. Digest until colorless or nearly so. Do not add either 
potassium permanganate or potassium sulfid. Dilute, neutralize, 
and distil as in the kjeldahl method. In neutralizing, it is conven- 
ient to add a few drops of phenolphthalein indicator, by which one 
can tell when the acid is completely neutralized, remembering 
that the pink color, which indicates an alkaline reaction, is de^ 
stroyed by a considerable excess of strong fixed alkali. The dis- 
tillation and titration are conducted as in the kjeldahl method. 
In distilling, the use of zinc or of some substance to prevent 
bumping or foaming is generally necessary. The amount of sul- 
furic acid recommended by Gunning is two grams for each gram 
of potassium sulfate ; but Van Slyke has found that this mixture 
is so viscous as to cause troublesome foaming frequently, and 
after cooling it cakes in a hard mass, which may be difificult to 
redissolve.^^ To avoid foaming and caking, he has found it an 
effective means to increase the amount of sulfuric acid used, 
using instead of two grams to one of potassium sulfate, three or 
four grams of acid to one of potassium sulfate. It is, therefore, 
suggested in carrying out the work, to use from five to 25 cubic 
centimeters (ordinarily about 20 cubic centimeters) of sulfuric 
acid for 10 grams of potassium sulfate. In case the potassium 
sulfate is not free from nitrogen compounds, one or two recrys- 
tallizations will make it pure. 

CHANGES IN KJELDAHL METHOD TO INCLUDE NITRIC ACID 

323. Modifications of Asboth. — In order to adapt the moist 

combustion process to nitric nitrogen Asboth proposed the use of 

benzoic acid.^^ For half a gram of saltpeter 1.75 grams of ben- 

'* Division of Chemistry, Bulletin 35, 1892 : 68. 
^^ Cheniisches Central-Rlatt, 1886 : 161. 



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374 



AGRICULTURAI4 ANALYSIS 



zoic acid should be used. At the end of the combustion the re- 
sidual benzoic acid is oxidized by means of potassium perman- 
ganate with a subsequent reheating. If the nitrogen be present 
as an oxid or as cyanid, one gram of sugar is added. The me- 
tallic element added is half a gram of copper oxid. Asboth also 
recommends that the soda-lye used in the distillation be mixed 
with sodium potassium tartrate for the purpose of holding the 
copper and manganese oxids in solution and thus preventing 
bumping. The alkaline liquor contains in one liter 350 grams 
of the double tartrate and 300 grams of sodium hydroxid. 

The principle on which the use of benzoic acid rests is found 
in the fact that it easily yields nitro-compounds and thus pre- 
vents the loss of the nitrogen oxids, these readily combining 
with the benzoic acid. The nitro-compounds can be subsequently 
converted into ammonia by treatment with potassium perman- 
ganate. 

The pyridin and chinolin groups of bodies do not yield all their 
nitrogen as ammonia by the above treatment. 

The conclusions drawn by Asboth from the analytical data ob- 
tained are : 

(i) Sugar should be used in the ordinary kjeldahl process in 
those cases where the nitrogen in the organic substance is pres- 
ent as oxids or as cyanogen. 

(2) In the case of nitrates good results may be secured with 
benzoic acid but permanganate must be added at the end. 

(3) The kjeldahl-wilfarth process can be ap])lied with sub- 
stances difhcultly decomposed, e. g., alkaloidal bodies. 

324. Variation of Jodlbauer. — The benzoic acid method, al- 
though a step forward, is not entirely satisfactory in the treat- 
ment of nitrates by moist combustion. Jodlbauer has proposed to 
substitute for the benzoic, phenolsulfuric acid.^^ 

From two- to five-tenths gram of a nitrate are treated with 
20 cubic centimeters of concentrated sulfuric and two and a 
half of phenolsulfuric acid, together with three grams of zinc 
dust and five drops of a solution of platinic chlorid of the strength 
mentioned above. The phenolsulfuric acid is prepared by dis- 

'« Chemisches Central-Blatt, 1886 : 433. 



DUTCH JODLBAUER METHOD 



375 



solving 50 grams of phenol in 100 cubic centimeters of strong 
sulfuric acid. The combustion is continued until the solution is 
colorless, which may take as much as five hours. If phosphoric 
anhydrid be used the time of the combustion may be diminished 
by one-half, but in such a case the glass of the combustion flask 
IS strongly attacked and is quite likely to break. 

When the substances used are very rich in nitrates, it is advis- 
able to rub them first with dry gypsum. 

The theory of the process rests on the fact that by a careful 
admixture of a nitrogenous substance diluted with land plaster 
with phenolsulfuric acid, it is possible to change the nitric acid 
into nitro-phenol, and by the reducing action of zinc dust to change 
the nitro-product formed into amido-phenol. This afterwards 
is transformed into ammonium sulfate by heating with sulfuric 
acid, by which process, at the same time, all other nitrogenous 
compounds present in the substance, as with Kjeldahl's method, 
likewise form ammonium sulfate, only with the difference that 
addition of mercury is here absolutely necessary for the com- 
plete transformation of the slowly decomposed amido-phenol, 
and this again brings about the necessity of decomposing the ni- 
trogenous mercury compounds formed in the solution by potas- 
sium sulfid, wliich is added after or with the soda-lye. 

325. The Dutch Jodlbauer Method.— The Royal Experiment 
Station of Holland directs that the jodlbauer process be carried 
out as indicated below. ^^ 

The reagents necessary are: 

1. Phcuohulfunc acid, prepared by dissolving 100 grams of 
pure crystallized phenol in pure sulfuric acid (1.84) and making 
up the solution to a liter with the same sulfuric acid. 

2. Zinc, carefully washed and thoroughly dried. 

3. Sodium hydroxid solution, the same as is used in the kjeld- 
ahl method. 

4. Potassium suWd solution, made by dissolving 355 grams of 
potassium sulfid (KoS), or sodium sulfid solution, made by dis- 
solving 250 grams of sodium sulfid (NaoS) in a liter of water. 

'■ Methoden van Onderzoek aan de Rijkslandbowproefstations voor 
het Jaar, 1894. 



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376 



AGRICULTURAL ANALYSIS 



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Oxidation flasks holding about 200 cubic centimeters, and dis- 
tillation flasks holding- about 750 cubic centimeters, both of Bo- 
hemian glass are used. 

Manipulation. — Moisten one gram of substance with water, dry 
and introduce into an oxidation flask. Cover with 15 cubic cen- 
timeters of phenolsulfuric acid and, after cooling, thoroughly mix 
by gently shaking. After five minutes add from two to three 
grams of zinc in small proportions, keeping the flask cool, then 20 
cubic centimeters of sulfuric acid, and finally two drops of 
mercury. Boil the mixture till the fluid is colorless, cool and 
dilute. Wash into a distillation flask and add an excess of sodium 
hydroxid solution and 25 cubic centimeters of the sodium (or 
potassium) sulfid solution. Distil and titrate as in the kjeldahl 
method. 

326. The Halle-Jodlbauer Method.— At the Halle Station it is 
the uniform practice to mix the nitrate with gypsum before 
the combustion. ^^ In the case of Chile nitrates 10 grams 
are rubbed with an equal amount of gypsum, and two grams of 
the mixture, equal to one gram of the nitrate, used for the 
determination. In the case of saltpeter mixtures which contain 
over eight per cent, of nitrogen, one gram of the mixture with 
gypsum is used, of guanos one and a half grams, and of lower 
forms of nitrates or mixtures thereof, from three to five grams. 

The sample, as prepared above, is treated with 30 cubic centi- 
meters of a mixture of phenolsulfuric acid and phosphoric 
anhydrid. The mixture is prepared by dissolving 66 grams of 
phenol and 250 grams of phosphoric anhydrid in strong sulfuric 
acid, and, after cooling, mixing the two solutions and making 
the volume up to 1650 cubic centimeters with pure sulfuric acid. 
The mixture contains, in 30 cubic centimeters, one and two-tenths 
grams of phenol and four grams of phosphoric anhydrid. In the 
use of phenolsulfuric acid the presence of phosphoric anhydrid 
is indispensable in keeping the sulfuric acid water-free and in 
absorbing the water produced by the combustion. 

*® lUeler und Schueidewind, Die agricultur-chcmische Versuchsstation 
Halle a/S, 1892 : 34. 



USK OF ZINC SULFID AND SODIUM THIOSULFATE) 



377 






The phenolsulfuric acid used contains only enough phenol 
to reduce half a gram of saltpeter. 

The sample and acid mixture having been put in the combus- 
tion flask, the latter is heated and shaken, at intervals, for an 
hour and the contents cooled. 

The conversion of the nitrates into nitro-phenol compounds is 
finished in this time, and the next step consists in reducing these 
bodies to the amido-phenol group. This is accomplished in the 
cold by nascent hydrogen produced by the addition of zinc dust 
to the mixture. From one to three grams of the dust are to be 
used in proportion to the quantity of nitrates originally present. 

The flask should be placed in a cooling mixture and the zinc 
dust added in small portions to prevent a too violent evolution 
of hydrogen. After the reduction is ended, the flask is allowed 
to stand for two hours, after which the combustion, distillation, 
and titration are accomplished in the usual way. On cooling, 
after the end of the combustion, the contents of the flask become 
solid. They may be brought again into the liquid state by shak- 
ing and gentle warming. 

327. The Salicylic Acid Method.— The introduction of the use 
of salicylic acid as the proper reagent to prevent the loss of 
n^*trogen when a nitrate is acted on by sulfuric acid is due to 
Scovell. It was noticed that the action of phenol was too violent 
to protect the process from loss of nitrogen. After a careful 
trial of many organic compounds capable of forming nitro-com- 
pounds in those circumstances, salicylic acid was selected as the 
most promising reagent.^^ Rigid trials by Scovell and others 
extending over many years have confirmed the propriety of 
this choice.2o The method has also been found to be accurate 
in the presence of chlorids as well as of nitrates. 

328. Use of Zinc Sulfid and Sodium Thiosulfate.— During 
the many analyses made by this modified method, it was 
noticed that on pure nitrates there was apparently a slight 

^' Thesis for Degree of Doctor of Philosophy, University of Illinois 
June, 1906, (Unpublished). 

^® Division of Chemistry, Bulletin 16, 1887 : 51. 
Division of Chemistry, Bulletin 19, 1888 : 47. 
New Jersey Agricultural Experiment Station Report, 1887, 169. 



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378 



AGRICULTURAL ANALYSIS 



THEORY 01^ THE) PROCESS 



379 



loss of nitrogen in adding the zinc dust. This was also a tedious 
part of the operation as the zinc dust had to be added gradually. 
Finely granulated zinc dust was tried, but in such cases the re- 
sults were invariably low. The results were lower when using 
chemically pure zinc dust instead of the commercial article. An 
investigation showed that the commercial zinc dust which had 
hitherto been used contained some zinc sulfid. This suggested 
that hydrogen sulfid might complete the reduction as well if not 
better than nascent hydrogen. Working on this theory, Scovell 
and Peter made a series of experiments, using zinc dust in one 
set of experiments and zinc sulfid in another set.^^ The results 
on pure potassium nitrate, containing a trace of water, and 
13.83 per cent, of nitrogen were as follows: 

Average 1376 

Theory 13.83 

The advantage of zinc sulfid over zinc dust is: First, the 
liability of the loss of nitrogen is not so great. Second, the 
zinc sulfid can be added all at once, and, therefore, it is less 
troublesome and more rapid than when the zinc dust is used. 
Third, the oxidation is more rapid and, as less salts are present, 
the distillation is more quiet. 

In 1893 sodium thiosulfate was substituted for zinc sulfid as 
the reducing agent in this method, not because better results 
were obtained, but because it was found to be difficult to get 
commercial zinc sulfid free from ammonia. The comparative re- 
sults obtained by the different chemists using these two reduc- 
ing agents were slightly in favor of zinc sulfid. 2- 

Otto Foerster gives the following as the reaction when sodium 
thiosulfate is used:^* 

4HN03-f4H2SO,-fNaoSo03= 
4HO.N02.S02+2NaHs6,+3H20. 

But it would be interesting to know whether hydrogen sulfid, 
which is also formed when salicylic acid and strong sulfuric acid 

5' Division of Chemistry, Rullelin 24, 1890 : 91. 
" Division of Chemistry, Bulletin 38, 1893 : 34. 
" Zeitschrift fur analytische Cheinie, 1889, 28 : 422. 



and nitrates are mixed, does not play at least a part in the re- 
duction of the nitro into the amido compounds. 

329. Theory of the Process. — The theory of the process by 
which salicylic acid converts nitrates to ammonia is as follows : 

1. When salicylic acid and sulfuric acid are added to a nitrate, 
the sulfuric acid takes up water and one of the hydrogen ele- 
ments of the salicylic acid is replaced by NOo, forming nitro 
salicylic acid. This reaction takes place without heat. It is 
probably mononitro and not dinitro salicylic acid that is formed. 
The reaction is probably as follows : 

(i) CeH,.OH.COJ-I+HN03+H2SO,= 
CeH,(N0,).0H.C0JT+H,S04+H,0. 

2. Subsequently when zinc sulfid is added the hydrogen sulfid 
liberated reduces the nitro salicylic acid to amido salicylic acid 
as follows : 

(2) CeH,(NO,).OH.CO,H+3H,S-kH,SO,+ 
CeH, ( NH.) .OH.CO,H+3S+2H,6+H,SO,. 

3. The strong sulfuric acid and heat on the amido salicylic acid 
breaks it up and there is formed ammonium sulfate, carbonic 
acid, sulfur dioxid and water, as follows : 

(3) 2CeH,(NH,).OH.CO.H-f28H,SO,= 
( NH, ) 2SO4+ i4CO,H-27SO,+32H,0. 

Similar reaction probably occurs when benzoic acid or phenol 
is used, but either nitro compounds are not as readily formed or 
they are not as easily converted into amido compounds, and pro- 
bably the heat caused by the reaction when phenol is used is the 
cause of the loss of some nitric acid. Inirthermore, phenol and 
benzoic acid do not break up as easily in the final reaction and, 
therefore, it takes longer to complete the oxidation than when 
salicylic acid is used. 

Other nitro- and amido-forming compounds might be sub- 
stituted for salicylic acid, but by the use of salicylic acid, the 
method is so simple and accurate that it is doubtful whether any 
substance other than salicylic acid would improve the method. 

Other substances have been under observation, e. g., pure potas- 
sium nitrate, using gallic acid in the place of salicylic acid, gave 



'II 









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380 



AGRICULTURAL ANALYSIS 



6.68 per cent, of nitrogen; pyrogallic acid, 8.21 per cent.; phenol, 
13.62 per cent.; benzaldehyde, 13.62 per cent.; phenyl salicylate, 
13.72 per cent. It is interesting to note that phenyl salicylate 
gave satisfactory results; the oxidation, however, is not as rapid 
as when saHcylic acid is used. 

For ease in manipulation, rapidity of work, and accuracy of 
results the salicylic acid method is to be recommended. 

330. The Official Kjeldalil Method for Nitric Nitrogen.— As 
has already been stated, the presence of certain organic com- 
pounds rich in hydrocarbons permits the reduction of nitric 
nitrogen to ammonia by combustion with sulfuric acid. Benzol, 
phenol, and salicylic acid have all been used for this purpose. 
The official chemists have adopted for their method the sali- 
cylic acid process first proposed by Scovell.^* 

Besides the reagents and apparatus given under the kjeldalil 
method there will be needed: 

(i) Zinc dust: This should be an impalpable powder; granu- 
lated zinc or zinc filings will not answer. 

(2) Sodium Mosul fate. 

(3) Commercial salicylic acid. 

It is found most convenient to prepare a solution of 33.3 grams 
of salicylic acid in one liter of the strongest sulfuric acid, and 
keep it for use rather than to mix it for each combustion. • 

The Manipulation. — Place from seven-tenths to three and five- 
tenths grams of the substance to be analyzed in a kjeldahl di- 
gesting f^ask, add 30 cubic centimeters of sulfuric acid containing 
one gram of salicylic acid, and shake until thoroughly 
mixed, then add five grams of crystallized sodium thiosulfate ; 
or add to the substance 30 cubic centimeters of sulfuric acid 
containing two grams of salicylic acid, then add gradually two 
grams of zinc dust, shaking the contents of the ilask at the same 
time. Finally place the flask on the stand for holding the diges- 
tion flasks, where it is heated over a low flame until all danger 
from frothing has passed. The heat is then raised until the 
acid boils briskly and the boiling continued until white fumes 
no longer escape from the flask. This requires about five or 10 

*-'♦ Division of Chemistry, Bulletin 16, 1887 : 51. 



GUNNING METHOD FOR NITRIC ACID 



381 



minutes. Add now approximately 0.7 gram of mercuric oxid 
or its equivalent in metallic mercury, and continue the boiling 
until the liquid in the flask is colorless or nearly so. In case the 
contents of the flask are likely to become solid before this point 
is reached, add 10 cubic centimeters more of sulfuric acid. Com- 
plete the oxidation with a little potassium permanganate in the 
usual way, and proceed with the distillation as described in the 
kjeldahl method. The reagents should be tested by blank experi- 
ments. The object of adding the sodium thiosulfate is to prevent 
the development of the amido-mercurous salts which require to 
be subsequently broken up by the addition of a sulfid. The reac- 
tion which takes place is represented by the following formula: 

^g<^ ^SO, + Na,SA..5H,0 = HgS + (NHj2SO,+Na,SO, 

IN Xlg 

-f4H20. The sodium thiosulfate may also be added after the 
digestion instead of the sodium sulfid.-'^ 

331. Gunning Method for Nitric Acid.— The essential features 
of this modification are due to Winton and Voorhees.-^ 
The modifications of the kjeldahl method, for similar purposes, 
furnished the material details for the gunning modified process. 
Winton reports good results from digesting for two hours from 
half a gram to a gram of the sample with 30 cubic centimeters 
of sulfuric containing two grams of salicylic acid, in a fiask of 
half a liter capacity. Two grams of zinc dust are then slowly 
added, with constant shaking, and the flask heated, at first gently, 
until, after boiling a few minutes, dense fumes are no longer 
emitted. Three grams of potassium sulfate are next added and 
the boiling continued until the solution is colorless, or, if iron be 
present, until a light straw color is produced. On cooling, when 
the mixture begins to solidify, water is added with caution, and 
afterwards sodium hydroxid, and the ammonia is obtained by 
distillation. 

In the process, as conducted by Voorhees, about one gram of 

2^ Neuberg, Beitrage zur cheiiiischen Physiologie und Pathologic, 1902, 

'* Connecticut Agricultural Experiment Station, Bulletin 112, 1892 • 1 
Division of Chemistry. Bulletin 35, 1892 : 86. 






li 



11 




g* 



i4% 



382 



AGRICULTURAL ANALYSIS 






the sample is digested with lo grams of potassium sulfate and 
30 cubic centimeters of sulfuric containing one gram of salicylic 
acid, and three grams of zinc sulfid. The heat is kept down until 
frothing ceases, and then the mass kept in gentle ebullition until 
clear. The distillation is accomplished with the usual precau- 
tions. The voorhees process is superior to that recommended 
by Winton in adding the potassium sulfate at the beginning of 
the combustion. 

332. Official Gunning Method Modified to Include the Nitro- 
gen of Nitrates.-^— In a digestion flask holding from 250 to 500 
cubic- centimeters place from 0.7 to 3.5 grams of the substance 
to be analyzed, according to the amount of nitrogen present. 
Add from 30 to 35 cubic centimeters of salicylic acid mixture; 
namely, 30 cubic centimeters of sulfuric to one gram of salicylic 
acid, shake until thoroughly mixed, and allow to stand from five 
tc 10 minutes, with frequent shaking; then add five grams of 
sodium thiosulfate and 10 grams of potassium sulfate. (It is 
suggested that after adding the sodium thiosulfate, the solution 
be heated for five minutes, cooled and the potassium sulfate 
added. This variation prevents foaming). Heat very gently 
until frothing ceases, then strongly until nearly colorless. Dilute,, 
neutralize, and distil as in the gunning method. 

DETERMINATION OF NITROGEN IN DEFINITE FORMS OF 

COMBINATION 

333. Introductory Considerations.— In the foregoing pages 
has been given a summary of the methods most in vogue for the 
estimation of nitrogen in fertilizers and fertilizing materials. 
There are many cases in which the analyst may have to deal 
with a definite chemical compound, and where a modified or 
shorter method may be used. There are other cases in which 
the nitrogen may be present in two or three definite forms, as in 
artificially mixed fertilizers, and where it is desirable to show 
the proportions in which the various forms are present. For 
these reasons it is necessary to be able to use methods by which 
the percentage of nitrogen in its various forms may be relatively^ 

" Bureau of Chemistry, Bulletin 107, 1907 : 8. 



DETERMINATION OF AMMONIA 



3^3 



as well as absolutely, determined. Such a case would be presented 
for instance, in that of a fertilizer containing dried blood, sodium 
nitrate, and ammonium sulfate. It is evident here that the total 
nitrogen could be determined by the volumetric method by com- 
bustion with copper oxid, or by the moist combustion process 
adapted to nitric nitrogen, but the method of determining the 
percentage of each constituent has not yet been described. 

We have to deal here with a case entirely similar to that of 
phosphoric acid in a superphosphate. There is no doubt what- 
ever of the uneven assimilability of the dififerent forms of nitro- 
gen. A nitrate, for instance, is already in condition for assimi- 
lation by plants. An ammoniacal salt is only partly changed to 
a state suited to plant nutrition, while organic nitrogen is forced 
to undergo a complete transformation before it becomes available 
to supply the needs of the growing plant. It is important, there- 
fore, equally to the analyst, the merchant and the agronomist, 
to know definitely the forms of combination in which the nitrogen 
exists and the relative proportion of the different combinations. 

334- Nitrogen as Ammonia. — The most frequent form in 
which nitrogen as ammonia is used for fertilizing is as sulfate. 
The method of determination to be described is, however, equally 
applicable to all ammonia salts. When no other form of nitrog- 
•enous compound is present the ammonia can be easily and di- 
rectly determined by distillation with soda- or potash-lye, as de- 
■scribed in the final part of the moist combustion process. 

335. Determination of Ammonia. — To one gram of the am- 
monia salt add from 200 to 300 cubic centimeters of water and 
30 grams of the soda-lye used in the moist combustion process ; 
distil, collect the ammonia, and titrate the excess of sulfuric acid 
exactly as there described. 

Fresenius recommends that the ammonia expelled by distilla- 
tion be taken up by a standard solution of sulfuric (hydrochloric, 
oxalic) acid, the excess of which is titrated with a standard solu- 
tion of soda or other alkali, using litmus as an indicator.^® If the 
distillate, on examination, be found to contain thiocyanate, soda- 

*" Chemical Quantitative Analysis, Cohn's Translation, from the 
Revised 6th German r:dition, 1904, 1 : 254. 



11 



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AGRICULTURAL ANALYSIS 



lye can not be used for the expulsion of ammonia, but in its place 
caustic magnesia is applied. 

In all cases where organic matter containing nitrogen is pres- 
ent, caustic magnesia must be substituted for the soda solution. 
The magnesia must be added in sufficient excess and the distil- 
lation continued a little longer than is necessary when soda-lye 
is used. Otherwise the details of the operation are the same. 

In a mixed fertilizer containing organic nitrogen and ammo- 
nia salts, the total nitrogen can be determined by the moist com- 
bustion process, and the ammoniacal nitrogen by distillation with 
magnesia. The difference between the two results will give the 
nitrogen due to the organic matter. 

To avoid any danger whatever of decomposing organic nitrog- 
enous compounds, the ammonia may be determined in the cold 
by treatment with soda-lye, under a bell-jar containing some set 
sulfuric acid. The operation must be allowed to continue for 
many davs. Even at the end of a long time it will be found that 
some ammonia is still escaping. It may, therefore, be finally in- 
ferred that all the nitrogen as ammonia is not obtained by this 
process, or that even magnesia may gradually convert other 
nitrogenous compounds into ammonia. In this connection the 
methods of determining ammonia in soils in paragraphs 450, 45 1 
and 452, Volume 1, may be consulted. 

336. Method of Boussingault.— The official French method 
is essentially the original method of Boussingault with slight 
modifications. It is conducted as follows t^^ In case the sam- 
ple is ammonium sulfate, about half a gram is placed in a flask 
of half a liter capacity, together with 300 cubic centimeters of 
distilled water and two grams of caustic magnesia. The flask- 
is connected with a condenser of glass or metal w^hich ends in a 
tube drawn out to a point and dipping beneath the set acid in 
the receiver in the usual way. The acid is colored with litmus 
or lacmoid tincture. The distillation is continued until about 
TOO cubic centimeters have gone over. The receiver is then re- 
moved with the usual precautions and the residual acid titrated. 
Suppose 20 cubic centimeters of normal acid have been employed 
2» Guide pour le Dosage de 1' Azote : 14. 



DE:Te:RM I NATION OF THIOCYANATKS 



385 



im 



and 12^ cubic centimeters of normal alkali be necessary to neu- 
tralize the excess of the acid. Then the nitrogen is found by 
the following equations: 20.0 — 12.5=7.5 and 7.5X0.014=0.105 
oram = w^eight of nitrogen found. Then 0.105X100^0.5=21 
=per cent, of nitrogen found. 

The distilling apparatus of Aubin is preferred by the French 
chemists, an apparatus so arranged with a reflux partial con- 
denser that nearly all the aqueous vapor is returned in a con- 
densed state to the flask, while the ammonia, on account of its 
great volatility, is carried over into the receiver. To avoid the 
regurgitation which might be caused by the concentrated ammo- 
nia gas coming in contact with the acid, the separable part of the 
condensing tube is expanded into a bulb large enough to hold 
all the acid which lies above its mouth. By means of this appara- 
tus the ammonia is all collected in the standard acid without 
greatly increasing its volume and the titration is thus rendered 
sharper. The employment of caustic magnesia has the advan- 
tage of not decomposing any organic matters or cyanids that may 
be present. 

If the sample under examination hold part of its ammonia a<=i 
ammonium magnesium phosphate, it will be necessary first to 
treat it with sulfuric acid in order to set the ammonia free, and 
then to use enough of the magnesium oxid to neutralize the ex- 
cess of the sulfuric acid and still supply the two grams necessary 
for the distillation. When the sample contains a considerable 
quantity of organic matter it sometimes tends to become frothy 
towards the end of the distillation. This trouble can be avoided 
by introducing into the flask one or two grams of paraffin. 

Where carbon dioxid is given off during the distillation, the 
contents of the receiver must be boiled before titration, or else 
lacmoid must be used as an indicator instead of litmus. 

337. Determination of Thiocyanates in Ammoniacal Fertilizers. 
— The extended use of ammonium sulfate as a fertilizer 
renders it important to determine the actual constituents which 
may be present in samples of this material. The following bodies 
have been found in commercial ammonium sulfates: Sulfuric 
acid, chlorin, ammonia, thiocyanic acid, potash, soda, lime and 
13 





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386 AGRICUI.TURAL ANALYSIS 

iron oxid. These are found in the soluble portions. In the in- 
soluble portions have been found silica, sulfates, lime, magnesia 
and iron oxid. A sample of commercial ammonium sulfate ana- 
lyzed by Jumeau contained the following substances :^^ 

Per Cent. 

Moisture 10.5109 

Aiiiiiioniuin sulfate • . - 67.8453 

Ammonium thiocyanate 9-3935 

Sodium sulfate 9-2429 

Potassium sulfate 0.9774 

Calcium sulfate 0.6800 

Iron thiocyanate 0.5000 

Magnesium chlorid traces 

Silica 0.0830 

Undetermined 0.7670 

The determination of the thiocyanic acid in the thiocyanate 
is generally made by the oxidation of the sulfur to sulfuric acid 
and its subsequent weighing in the form of barium sulfate. 
Jumeau has modified the method by determining the amount of 
the thiocyanate by means of a titrated liquid. The method is 
practiced as follow^s: 

A solution of ammonium thiocyanate is prepared, containin;^ 
eight grams of this salt per liter, and its exact content of thio- 
cyanate is rigorously determined by titration with silver nitrate 
or by the weight of the barium sulfate produced after the oxida- 
tion of the sulfur. Ten cubic centimeters of the titratecl liquor 
are diluted with water to about 100 cubic centimeters and 10 
cubic centimeters of pure sulfuric acid added. Afterward, drop 
by drop, a solution of potassium permanganate is added, con- 
taining about 10 grams of that salt per liter. The perman- 
ganate is instantly decolorized. There is an evolution of hydro- 
cyanic acid as the thiocyanate passes to the state of sulfuric acid., 
A single drop in excess gives to the mixture the well-known rose 
coloration of the permanganate solution which persists for sev- 
eral hours. The number of cubic centimeters necessary to pro- 
duce the persistent rose tint is noted and the same operation is 
carried on with from one-half to one gram of the unknown prod- 
uct which is to be assayed. A simple proportion indicates the 
^ Revue de Chimie analytique appliqu^e, 1893, 1:51. 



SEPARATION OF PROTKID 



387 



content of the thiocyanate in the unknown body. The process 
is of great exactitude and permits the rapid determination of 
thiocyanic acid in the presence of chlorids, cyanids, etc., which 
remain without action upon the permanganate. In case chlorids 
and cyanids are absent the thiocyanate can be determined directly 
by silver nitrate either by weighing the precipitate or by the pro- 
cess of Volhardt, based upon the precipitation of the silver by 
thiocyanate in the presence of a ferric salt. The end of the 
reaction is indicated by the red coloration which the liquid shows 
when the thiocyanate is in excess. 

338. Separation of Proteid from Amid and Other Forms of 
Nitrogen in Organic Fertilizers. — It may be of interest to the 
dealer, farmer, and analyst to discriminate between the proteid 
and other nitrogen in fertilizers, such as oil-cakes, etc. The final 
value of the nitrogen for plant nourishment is not greatly dif- 
ferent, but the immediate availability for the use of plants is a 
matter of some importance. The most convenient process in such 
a case is the copper hydroxid separation process as improved by 
Stutzer.^^ The process is conveniently carried out in accordance 
with the method prescribed by the official chemists.^- 

Total Crude Protein. — Determine nitrogen as directed for nitro- 
gen in fertilizers and multiply the result by 6.25 for the crude 
protein. 

Determination of Albuminoid Nitrogen. — To 0.7 gram of the 
substance in a beaker add 100 cubic centimeters of w^ater, heat 
to boiling, or, in the case of substances rich in starch, heat on 
the water bath 10 minutes, and add a quantity of cupric hydroxid 
mixture containing one-half gram of the hydroxid; stir thor- 
oughly, filter when cold, wash with cold water, and put the filter 
and its contents into the flask containing the concentrated sulfuric 
acid for the determination of nitrogen. The filter papers used 
must be practically free of nitrogen. Add sufficient potassium 
sulfid solution to completely precipitate all copper and mercury, 
and proceed as in the moist combustion process for nitrogen. If 

■^* Journal fiir Landwirtschaft, 1880, 28 . 103. 

Chemiker-Zeitung, 1880, 4 : 360. 
•*^ Bureau of Chemistry, Bulletin 107, 1907 : 38. 



m 



388 



AGRICULTURAL ANALYSIS 



i 



the substance examined consists of seed of any kind, or residues 
of seeds, such as oil-cake or anything else rich in alkaline phos- 
phates, add a few cubic centimeters of a concentrated solution 
of alum free from ammonia just before adding the cupric hy- 
droxid, and mix well by stirring. This serves to decompose the 
alkaline phosphates. If this be not done, cupric phosphate and 
free alkali may be formed, and the protein-copper precipitate 
may be partially dissolved in the alkaline liquid. 

Cupric Hydroxid.—Fvtpavt the cupric hydroxid as follows: 
Dissolve lOO grams of pure cupric sulfate in five liters of water, 
and add 2.5 cubic centimeters of glycerol; add a dilute solution 
of sodium hydroxid until the liquid is alkaline; filter, rub the 
precipitate up with water containing five cubic centimeters of 
glycerol per liter, and wash by.decantation or filtration until the 
washings are no longer alkaline. Rub the precipitate up again in 
a mortar with water containing 10 per cent, of glycerol, thus 
preparing a uniform gelatinous mass that can be measured out 
with a pipette. Determine the quantity of cupric hydrate per 
cubic centimeter of this mixture. 

Amid Nitrogen. — The albuminoid nitrogen determined as above 
subtracted from the total gives that part of the organic nitrogen 
existing in the sample as amids and in other allied forms. 

339. Separation of Nitric and Ammoniacal from Organic Nitro- 
gen.— The nitrogen being present in three forms, viz., organic, 
ammoniacal and nitric, the separation of the latter two may be ac- 
complished by the following procedure :'•' One gram of the fer- 
tilizer is exhausted on a small filter with a two per cent, solu- 
tion of tannin, using from 30 to 40 cubic centimeters in small 
portions. This is sufficient to dissolve all the nitrates and the 
greater portion of the ammoniacal salts, while the tannin ren- 
ders insoluble all the organic nitrogenous compounds. The filter 
and its contents are treated for nitrogen by the kjeldahl process. 
When the distillation and titration are completed the solution 
obtained by the aqueous tannin is added to the distilling flask 
and the operation continued. This represents the ammoniacal 
nitrogen. 

3» Aubiu et Quenot, Bulletin de la Soci^t^ chimique de Paris, 1890, [3], 
3 : 324- 



11 



METHOD OF DETERMINING NITROGEN 



389 



The nitric acid is estimated by the ferrous iron or other appro- 
priate method, to be described further on, in another portion of 
the substance. 

340. Method of French Commission for Determining Nitrogen. 

— Several methods are proposed by this commission for the 
determination of nitrogen.^* The old method of combustion with 
soda-lime which is conducted according to the general principles 
is described in full. When the nitrogen is to be determined in sub- 
stances which are not homogeneous and which it is difficult to 
reduce to a powdered state, a modification of the process, due to 
Grandeau, is employed. Such substances are, for instance, pieces 
of cloth, leather, wool, horns and hair. It is almost impossible 
to obtain a homogeneous mixture of such bodies. Large quan- 
tities of them are, therefore, according to this method, treated 
with sulfuric acid and then heated until the decomposition is 
complete and they are easily reduced to a homogeneous mass. 
This is best secured by adding some finely powdered gypsum. 
When the decomposition is completed and a homogeneous mass 
is secured, the rest of the process is conducted by the usual 
methods. 

The French commission also recommends the common method 
already described for the determination of nitrogen in an organic 
state by the process of Kjeldahl, and of nitrogen in the nitric 
state and of sulfate of ammonium by the methods usually em- 
ployed. 

341. Method of Determining Nitrogen Adopted by the Union of 
German Fertilizer Manufacturers. — Nitric Nitrogen. — The nitro- 
gen in the form of nitrates is determined by the method of Ulsch 
and Devarda.^^ 

Ammoniacal Nitrogen. — This is determined in the usual way 
by titration with an alkali. Freshly burned magnesia hydrate is 
employed as an alkaline reagent, although lime may also be 
used where little or no organic matter is present, and the am- 
monia is mostlv in the form of ammoniacal salt. Soda-lve should 
^* Grandeau, Traite d' Analyse des Matieres agricoles, 3d Edition, 1897, 

1 ; 427. 

^^ Methoden ziir Untersuchnngder Kiinstdiin^eniittel, T903 : 15. 



i i; i 






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390 



AGRICULTURAI, ANALYSIS 



only be used when it is certain that no organic nitrogen is present. 
The ammonia is collected in set sulfuric acid, and, as an indicator, 
it is recommended to use paranitro-phenol solution in the pro- 
portion of one to 10 of alcohol. Tincture of cochineal or congo 
red in water is also permitted. 

Organic Nitrogen. — The method of Kjeldahl, with its modern 
modification for the inclusion of nitric nitrogen, is recommended. 

342. Estimation of Perchlorate in Chile Saltpeter. — Attention 
is called to the occasional occurrence m Chile saltpeter of 
potassium perchlorate. The method employed depends upon the 
determination of the chlorin content of the material under inves- 
tigation both before and after the decomposition of the perchlo- 
rate. The conversion of perchlorate of potassium is secured by 
simple ignition or by ignition after the addition of different re- 
agents, as, for instance, metallic lead, caustic lime, sodium car- 
bonate, magnesium oxid, etc. The following method is recom- 
mended as satisfactory and easily carried out.^^ 

In this method five grams of Chile saltpeter, in which the 
amount of chlorin has been determined, is placed in a porcelain 
crucible of about 40 to 50 cubic centimeters capacity with from 
15 to 20 grams of lead borings and submitted to a gradually in- 
creased heat. When the salt and the lead are melted, the mass 
is vigorously stirred with a copper wire with a regulation of the 
heat so as not to secure a too rapid evaporation of the mass. 
When the mass begins to thicken and only a few bubbles of gas 
are escaping, the heat is raised to a dark red on the bottom of 
the crucible and held at this temperature for one or two minutes. 
After cooling, the melt, which now contains nitrate and chlorate, 
is softened with hot water and washed into a beaker. Three or 
four grams of carbonate of soda are added and the mixture 
gradually warmed. After filtration nitric acid is added to the 
filtrate to acidity, and the chlorin estimated in the usual way with 
the nitrate of silver. 

From the amount of chlorin obtained, that which was originally 
present is subtracted and the difference is the chlorin due to 

•^' Selcktnann, Zeitschrift fiir aiigewaiidte Chemie, 1898, 11 : loi. 



METHOD OF SCHI.0ESING 



391 



perchlorate. One equivalent of silver nitrate corresponds to one 
equivalent of potassium perchlorate. 

343. Method of Blattner-Brasseur.^^ — In this method five grams 
of saltpeter, which has been freed from moisture by heat- 
ing to 150°, are treated with from seven to eight grams of 
pure chlorin-free calcium hydrate in a porcelain or platinum 
crucible of about 25 to 30 cubic centimeters capacity and the 
covered crucible heated for 15 minutes over a bunsen. The ig- 
nited mass is dissolved and neutralized with nitric acid and the 
chlorin titrated with nitrate of silver or estimated by the gravi- 
metric method as above described. 

THE NITRIC ACID PROCESS 

344. Occurrence of Highly Oxidized Nitrogen. — The nitrogen 
of fertilizers, soil waters, etc., often exists in a highly oxidized 
state as nitrous or nitric acid or compounds thereof. The fol- 
lowing paragraphs are devoted to the description of methods 
employed for estimating nitrogen in these states of combination 
and the principles on wdiich they are based. The processes for 
estimating nitrogen by combustion with copper oxid and by 
moist combustion with sulfuric acid have both been used for the 
determination of the quantity of nitrogen existing in a highly . 
oxidized state. These processes have been fully discussed under 
their proper heads. In the case of soil extracts, drainage waters, 
etc., it will be sufficient to discuss, for the present, only those pro- 
cesses adapted especially to a quick and accurate estimation of 
oxidized nitrogen when occurring in relatively small quantities. 

345. Method of Schloesing. — The principle of the method of 
Schloesing depends on the decomposition of nitrates in the pres- 
ence of a ferrous salt and a strong mineral acid.^^ The nitrogen 
in the process appears as nitric oxid, the volume of which may 
be directly measured, or it may be converted into nitric acid and 
titrated by an alkali. 

^^ Cheniiker-Zeitung, 1900, 24 : 767. 

^^ Aniiales de Chimie et de Physique, 1854, [3], 40 : 479. 
Zeitschrift fiir aiialytische Chemie, 1870, 9 : 24. 
Die landwirtschaftlicheu Versiiclis-Stationen, 1869, 12 : 164. 
Journal of the Chemical Society, 1880, 37 1468; 1882, 41 : 345; ^^^9* 
55 : 537. 



i( 



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392 



AGRICULTURAL ANALYSIS 



The typical reactions which take place are represented in the 
following equation : 

6FeCl2+2KN03+8HCl=3FeXle+2KCI+4H,0+2NO. 
346. Schloesing's Modified Method. — The schloesing method 
as now practiced by the French chemists is conducted in the ap- 
paratus shown in Fig. 20.^'^^ The carbon dioxid is generated by 
the action of the hydrochloric acid in F on the fragments of 
marble in A. After passing the wash-bottle, the gas enters the 
small tubulated retort, C, which contains the nitrate in solution. 
When the quantity of nitrate is small, as in ordinary soils, 100 
grams are placed in an extraction flask, plugged with cotton, and 

H 




Fig, 20. Schloesing's Apparatus for Nitric Acid. 

a layer of the same material is placed over the soil for the pur- 
pose of securing an even distribution of the extracting liquid. 
This liquid is distilled water containing: in each liter one gram 
of calcium chlorid. The purpose of using the calcium chlorid is 
tc prevent the soil from becoming compacted, which would ren- 
der the extraction of the nitrate difficult. The extracting liquid 
is allowed to fall, drop by drop, from a mariotte bottle until the 
filtrate amounts to 500 cubic centimeters. This volume is con- 
centrated on a sand-bath until it is reduced to 10 or 15 cubic cen- 
timeters, when it is transferred to a flat-bottomed dish and the 
evaporation finished over steam, care being taken not to allow 
the temperature to exceed 100°. 

^* Encyclopedia chiniique, 1888, 4 : 151. 



FRENCH AGRICULTURAL ME:TH0D 



393 



Another and more rapid method for dissolving the nitrate may 
also be practiced. In a flask holding about one liter, place 220 
grams of the soil and 660 cubic centimeters of distilled water and 
shake vigorously, or enough water to make 660 cubic centimeters 
together with the moisture remaining in the air-dried sample 
taken. All the nitrates pass into solution. Throw the contents of 
the flask into a filter and use 600 cubic centimeters of the filtrate, 
which will contain all the nitrates in 200 grams of the sample 
taken. This filtrate is evaporated as described above. 

In the flat dish containing the dried nitrates pour three or four 
cubic centimeters of ferrous chlorid solution and stir with a small 
glass rod until complete solution of the nitrates takes place. By 
means of a small funnel the solution is poured into C, and the 
capsule and funnel are well rinsed with two cubic centimeters of 
hydrochloric acid. The washing is repeated three times, as above 
described, and once with one cubic centimeter of water, which is 
added cautiously so as to form a layer over the surface of the 
heavier liquid. The tubulated flask is then connected with the 
carbon dioxid apparatus, previously freed from air, and the gas 
allowed to flow evenly until the whole of the interior of the ap- 
paratus is completely air-free. The other details of the method 
are essentially the same as those adopted by the Commission of 
French Agricultural Chemists, which will be given below. 

347. The French Agricultural Method. — The Schloesing method, 
as practiced by the French agricultural chemists, is very 
slightly diflferent from the procedure just described.^^ The pro- 
cess with soils and fertilizers poor in nitrogen is carried on as 
follows : 

Five hundred grams of the sample are introduced into a flask of 
about two liters capacity and shaken thoroughly with a liter of 
distilled water. The whole of the nitrates of the soil is thus 
brought into solution. The solution is filtered ana 400 cubic cen- 
timeters of the filtrate are used, which correspond to 200 grams 
of the soil. This liquid is evaporated in a flask, adding a frag- 
ment of paraffin to prevent foaming, until its volume is reduced 
to 15 or 20 cubic centimeters. It is afterwards transferred through 
*^ Annales de la Science agronomique, 1891, 1 : 263. 









'§ 



''^ 



i'm 



Ih 












f 
lis. 



394 



AGRICULTURAL ANALYSIS 



FRENCH AGRICULTURAL METHOD 



395 



a filter into a capsule with a flat bottom, in which the evapora- 
tion is finished on a steam-bath, taking; care that the tempera- 
ture does not exceed ioo°. An important precaution is not to 
allow the contact of the water with the soil to be too prolonged, 
to avoid the reduction of the nitrates which could take place 
under the influence of the denitrifying organisms which are de- 
veloped with so great a rapidity in moist earth. The apparatus 
in which the transformation of the nitrates into nitric oxid takes 
place is essentially that already described (Fig. 20). The car- 
bon dioxid generator is connected by means of a rubber tube 
and a small wash-bottle to the small retort in which the reaction 
takes place, and from which the exit tube leads to a mercury 
trough. The gas which is disengaged is received under a jar 
drawn out to a fine point in its upper part, which carries about 
15 cubic centimeters of potash solution containing two parts of 
water to one of potash. 

The operation is conducted as follows : 

Into the small capsule which contains the dried matter, three 
or four cubic centimeters of ferrous chlorid are poured. By 
means of a stirring rod the residue sticking to the sides of the 
capsule is detached with care, and all the matter is thus collected 
in the bottom. By means of a small funnel the contents of the 
capsule are introduced into the retort. About two cubic centi- 
meters of hydrochloric acid are used for washing out the mate- 
rials, and this acid is also introduced into the retort. The wash- 
ing with hydrochloric acid is repeated three or four times, and 
finally the apparatus is washed with one cubic centimeter of 
water, which is also poured in by the small funnel with great 
care, so that this water may form a layer over the surface of the 
liquid. The apparatus is now connected and filled completely 
with carbon dioxid. Since it is necessary that this gas should 
be completely free of air, the flask which generates it is first 
filled with the acidulated water from the acid flask, and the air 
is thus almost totally displaced by the liquid. The evolution of 
carbon dioxid gas which follows, completely frees the apparatus 
from air. When this is accomplished the retort is connected 
with the rest of the apparatus and the gas allowed to pass for 



about two minutes until the air is completely driven out of all 
the connections. The current is arrested for a moment by pinch- 
ing the rubber tube which conducts the carbon dioxid into the 
retort, and the vessel which is to receive the gas is then placed 
over the delivery tube, this vessel being filled with mercury and 
a strong solution of potash. The communication between the 
retort and the carbon dioxid flask is broken and the flask is 
heated slightly by means of a small lamp. The first bubbles of 
gas evolved should be entirely absorbed by the potash. This will 
be an indication of the complete absence of the air. When the 
liquid is in a state of ebullition the nitrogen dioxid is set free. 
The boiling is regulated in such a way that the evolution is reg- 
ular and the liquid of the retort may not, by a too violent boiling, 
pass into the receiver. The boiling is continued until the larger 
part of the liquid is distilled and only three or four cubic centi- 
meters remain in the retort. At this time a few bubbles of carbon 
dioxid are allowed to flow through in order to cause to pass into 
the receiver the last traces of nitric oxid. The gas received is left 
for some minutes in contact with the potash. 

Afterward, in a small flask, G, the neck of which is drawn out 
to a fine point, and carrying a bulb-tube, H, and a piece of rub- 
ber tubing, there are boiled 25 or 30 cubic centimeters of water 
for five or six minutes in order to drive all the air out of the 
flask, and while the boiling is continued the rubber tubing is 
fastened to the drawn-out part of the jar containing the nitric 
oxid. Within the rubber tubing the drawn-out point is broken 
and the vapor of water is forced into the jar and drives before 
it the solution of potash which has filled the capillary part of 
the drawn-out tube. As soon as the point is broken, the boiling 
of the flask is stopped and by its cooling the nitric oxid passes 
into it. It is necessary to press the rubber tubing with the fingers 
in order that the passage of the gas into the flask be not too rapid. 
As the solution of potash rises in the bell-jar which contains the 
nitric oxid near to the point where the rubber tubing covers its 
drawn-out portion, the fingers are removed and a clamp put in 
their place. There still remains a little nitric oxid in the flask, 
and to drive this out it is necessary to introduce five or six cubic 



!« 



?iV 



.3!' 







>l\, 

m 



39^ 



AGRICUVrURAL, ANALYSIS 



centimeters of pure hydrogen, which are allowed to pass over 
into the receiving flask by releasing the clamp in the same way 
as for the nitric oxid. The hydrogen being introduced in succes- 
sive portions, finally carries all the nitric oxid into the flask with- 
out allowing any of the potash to enter. 

The flask containing the nitric oxid is now connected with a 
reservoir of oxygen. The oxygen is allowed to enter, bubble by 
bubble, meanwhile cooling the flask by immersion in water. The 
transformation of nitric oxid into nitric acid is not entirely com- 
plete until after 24 hours. It is necessary, therefore, to wait so 
long after the introduction of the oxygen before determining 
the amount of nitric acid produced. 

The contents of the flask are placed in a titration-jar, the flask 
being washed two or three times and a few drops of tincture of 
litmus being added. The nitric acid is then determined by a 
standard solution of calcium hydroxid or some other standard 
alkali. From the titration the content of nitric acid is calcu- 
lated. 

The French committee further suggests that this method may 
be modified in the way of making it more rapid by collecting 
the nitric acid in a graduated tube filled with mercury and con- 
taining some potash. The volume of the gas is determined and 
the pressure of the barometer together with the temperature are 
observed ; then the usual calculations are made to reduce the vol- 
ume to zero and to a pressure of 760 millimeters of mercury. 
Each cubic centimeter of nitric oxid thus measured corresponds 
to 2.417 milligrams of nitric acid. The presence of organic mat- 
ter does not interfere with the determination of nitric acid by 
either of the methods given above. 

348. Method of the French Sugar Chemists.— The nitrogen 
in Chile saltpeter is estimated by the French chemists according 
to the method of Schloesing. In order to avoid the trouble of 
calculating the results from the volume of nitric oxid obtained, 
a determination is first made with a pure salt, sodium or potassium 
nitrate. The volume of gas obtained is read directly without 
correction and used for direct comparison, which is made as 
follows : 



METHOD OF SCHLOESING-WAGNER 



397 



The solutions of the pure salts and of the sample to be analyzed 
are made of such a strength as to contain 66 grams of sodium 
nitrate, or 80 grams of potassium nitrate, in a liter. Five cubic 
centimeters of such a solution will yield a little less than 100 
cubic centimeters of nitric oxid under usual conditions. Let 
the volume of gas obtained with the pure salt be v, and that 
with the sample be v\ The calculation is then made from the 



V 



X 



equation : 
^ V 100 

Example. — Let 95 cubic centimeters be the volume of gas from 
five cubic centimeters of the pure salt (sodium nitrate), and 91.5 
cubic centimeters be the volume of gas from five cubic centi- 



91.5 



X 



meters of the sample; then — ~ = , whence x = 96. -^i. 

95 100 

Hence the sample analyzed contains 96.31 per cent, of sodium 

nitrate. Since the pure sodium nitrate contains 16.47 P^^ cent, of 

nitrogen.the sample under examination would contain — — — 

100 

=: 15.86 per cent. 

It is evident that this comparative method is quite easy of ap- 
plication when the sample under examination has no other nitrate 
in it except that combined with the one base. 

349. Method of Schloesing-Wagner. — The schloesing-wagner 
method for estimating nitrogen in the nitrates of fertilizers is 
carried out at the Halle experiment station as follows :*^ 

A flask, Fig. 21, of about 250 cubic centimeters capacity, is 
provided with a rubber stopper with two holes. Through one 
of them is passed the stem of a funnel carrying a glass stop-cock. 
The other carries a delivery tube leading to the receiving vessel. 
The end of the delivery tube is bent so as to pass easily under 
the mouth of the measuring burette and is covered with a piece 
of rubber tubing. 

Fifty cubic centimeters of saturated ferrous chlorid solution 

and the same quantity of 10 per cent, hydrochloric acid are 

placed in the flask. The ferrous chlorid solution is obtained 

*' Bielerand Schiieidewind, Die agricultur-chemische Versuchsstation, 
Halle a/S, 1892 : 51. 



Mi 



11 



:4i 4 






m 






m 



'i'i If 



.P5 



I': 






^K 
•'*■, 



^1 



I 






;!:* 



m 

"9' ' 

I 
I 

III 

if 



'"-■\ 



398 



AGRICULTURAI, ANALYSIS 



MODII^ICATION 0]P WARINGTON 



399 



by dissolving nails or other small pieces of iron in hot hydro- 
chloric acid and it is kept in glass stoppered flasks, of about 50 
cubic centimeters capacity, entirely filled. The content of one 
flask is enough for about 12 determinations and by using the 
whole content of a flask as soon as possible after opening, any 
danger of oxidation, which would take place in a large flask 
frequently opened, is avoided. 

The contents of the flask are boiled until all the air is driven 
off. The delivery tube is then placed under the measuring 
tube, which is filled with 40 per cent, potash-lye. The measur- 
ing tube is previously almost filled with potash-lye and then a 

\ 





Fig. 21. Schloesing-Wagner Apparatus. ^ 

few drops of water added and the tube covered with a piece of 
filter paper. By a careful and quick inversion the measuring 
tube can be brought into the vessel receiving it without any dan- 
ger of air entering. The boiling is continued for some time and 
when no more air escapes, the end of the delivery tube is brought 
into another freshly filled measuring tube and the estimation is 
commenced. 

Ten cubic centimeters of a normal saltpeter solution, contain- 
ing two and a half grams of pure sodium nitrate in 100 cubic 
centimeters are placed in the funnel and, with continued boiling, 
allowed to pass, drop by drop, into the flask. When almost all 
has run out the funnel is washed three times with 10 cubic cen- 



timeters of 10 per cent, hydrochloric acid and this is allowed to 
pass, drop by drop, into the flask. When no more nitric oxid is 
evolved the measuring tube is transferred to a large jar filled 
with distilled water. 

The solution of the substance to be examined should be used 
in such quantity as will give about the same quantity of gas 
as is furnished by the 10 cubic centimeters test nitrate solution 
before described ; viz., about 70 cubic centimeters. Eight 
or 10 determinations can be made, one following the other, and 
finally another determination with normal sodium nitrate 
solution should be made as a check. At the end of the opera- 




Fig. 22. Warington's Apparatus for Nitric Acid. 

tion all of the measuring tubes are in the large jar filled with 
distilled water. The temperature of the surrounding water will 
soon be imparted to the contents of each tube and the volume of 
nitric oxid is read by bringing the level within and without the 
measuring-tube to the same point. The percentages are calcu- 
lated for the given temperature and barometer pressure in the 
usual way; or to avoid computation, the volume can be com- 
pared directly with the volume furnished by the normal nitrate 
solution, which is a much simpler method. 

350. Modification of Warington. — The method of procedure 
and description of apparatus used, as employed by Warington, 
are as follows: 

The vessel in which the reaction takes place is a small tubu- 
lated receiver, A (Fig. 22), about four centimeters in diame- 



J I 









%i 



. 






^1 

{ ff 
H 



400 



AGRICULTURAL ANALYSIS 



4 



I 



P 
'k 

•■1 



ter, mounted and connected as shown in the illustration. The 
delivery tube dips into a jar of mercury in a trough containing 
the same liquid. The long supply funnel-tube a is of small 
bore, holding in all only one-half cubic centimeter. The con- 
necting tube, F, carrying a clamp, is also of small diameter and 
serves to connect the apparatus with a supply of carbon dioxid. 
In practice, the supply tube a is first filled with strong hydro- 
chloric acid and carbon dioxid passed through the apparatus un- 
til the air is all expelled. This is indicated when a portion of the 
gas collected over the mercury, is entirely absorbed by caustic 
alkali. 

At this point the current of carbon dioxid is stopped by the 
clamp C, and a bath of calcium chlorid, B, heated to 140'' is 
brought under the bulb A, until the latter is half immersed 
therein. The temperature of the bath is maintained by a lamp. 
By allowing a few drops of hydrochloric acid to enter the receiver, 
the carbon dioxid is almost wholly expelled. The end of the 
delivery tube is then connected with the tube, T, filled with 
mercury, and the apparatus is ready for use. 

The nitrate, in which the nitric acid is to be determined, in a 
dry state, is dissolved in two cubic centimeters of the ferrous 
chlorid solution (one gram of iron in 10 cubic centimeters), one 
cubic centimeter of strong hydrochloric acid is added, and the 
whole is then introduced into the receiver through the supply- 
tube, being followed by successive rinsings with hydrochloric 
acid, each rinsing not exceeding one-half cubic centimeter. The 
contents of the receiver are, in a few moments, boiled to dryness ; 
a little carbon dioxid is admitted before dryness is reached, and 
again afterwards to drive over all remains of nitric oxid. In 
the recovered gas the carbon dioxid is first absorbed by caustic 
potash, and afterwards the nitric oxid by ferrous chlorid. All 
measurements of the gas are made in Frankland's modification 
of Regnault's apparatus. The carbon dioxid should be as free 
as possible from oxygen. The carbon dioxid generator is formed 
of two vessels, the lower one consisting of a bottle with a tubule 
in tl:e side near the bottom ; this bottle is supported in an inverted 
position and contains the marble from which the gas is generated. 



MODIFICATION OF WARINGTON 



401 



The upper vessel consists of a similar bottle standing upright and 
containing the hydrochloric acid required to act on the marble. 
The two vessels are connected by a glass tube passing from the 
side tubule of the upper vessel to the inverted mouth of the lower 
vessel. The acid from the upper vessel thus enters below the 
marble. Carbon dioxid is generated and removed at pleasure 
by opening a stop-cock attached to the side tubule of the lower 
vessel thus allowing hydrochloric acid to descend and come in 
contact with the marble. A good Kipp's generator of any ap- 
proved form may also be used instead of the simple apparatus 
above described. 

The fragments of marble used are previously boiled in water 
in a strong flask. After boiling has proceeded for some time, a 
rubber stopper is fixed in the neck of the flask and the flame 
removed. Boiling will then continue for some time in a partial 
vacuum. 

The hydrochloric acid is also well boiled and has dissolved in 
it a moderate quantity of cuprous chlorid. As soon as the acid 
has been placed in the upper leservoir, it is covered by a layer 
of oil. The apparatus being thus charged is at once set in active 
work by opening the stop-cock of the marble reservoir ; the acid 
descends, enters the marble reservoir, and the carbon dioxid 
produced drives out the air. As the acid reservoir is kept on a 
higher level than the marble reservoir, the latter is always under 
internal pressure, and leakage of air from without, into the ap- 
paratus, can not occur. 

The presence of the cuprous chlorid in the hydrochloric acid 
not only insures the removal of dissolved oxygen, but aflfords an 
indication to the eye of the maintenance of this condition. While 
the acid remains of an olive tint, oxygen is absent; but should 
the color change to a blue-green, more cuprous chlorid must 
be added. All the reagents employed should be previously boiled. 

In order to secure absolute freedom from air, the following 
modifications on the above process have been adopted by War- 
ington. The apparatus having been mounted as described, the 
funnel-tube attached to the bulb retort is filled with water, and 
the apparatus connected with the carbon dioxid generator. Car- 



H 

4 



i 






402 



AGRICULTURAL ANALYSIS 



r 



it 



:i 



bon dioxid is then passed through the apparatus until a moder- 
ate stream of bubbles rise in the mercury trough. The stop- 
cock is left in this position, and the admission of gas is con- 
trolled by the pinch-cock. The bath of calcium chlorid is so 
adjusted as to cause the bulb retort to be almost entirely sub- 
merged, and the temperature of the bath is kept at 130° to 140°. 
Small quantities of water are next admitted into the bulb and 
expelled as steam in the current of carbon dioxid, the supply 
of this gas being shut off before the evaporation is entirely com- 
pleted, so as to leave as little carbon dioxid as possible in the 
apparatus. Previous to very delicate experiments it is advisable 
to introduce through the funnel-tube a small quantity of potas- 
sium nitrate, ferrous chlorid, and hydrochloric acid, rinsing the 
tube with the latter reagent. Any trace of oxygen remaining 
in the apparatus is then consumed by the nitric oxid formed ; 
and after boiling to dryness and driving out the nitric acid with 
carbon dioxid, the apparatus is in a perfect condition for a quan- 
titative experiment. 

351. Preparation of the Materials to be Analyzed. — According 
to Warington, soil extracts may be used without other preparation 
than concentration. 

Vegetable juices which coagulate when heated require to be 
boiled and filtered or else evaporated to a thin sirup, treated, 
with alcohol, and filtered. A clear solution being thus obtained, 
it is concentrated over a water bath to a minimum volume in a 
beaker of small size. As soon as cool, it is mixed with one 
cubic centimeter of a cold saturated solution of ferrous chlorid 
and one cubic centimeter of hydrochloric acid, both reagents 
having been boiled and cooled immediately before use. 

In mixing with the reagents, care must be taken that bubbles 
of air are not entangled, which is apt to occur with viscid extracts. 
The quantity of ferrous chlorid mentioned is amply sufficient 
for most extracts, but it is well to use two cubic centimeters 
in the first experiment, the presence of a considerable excess of 
ferrous chlorid in the retort being thus insured. With l)ulky 
vegetable extracts more ferrous chlorid should be employed. 
To the sirup from 20 grams of mangel-wurzel sap, five cubic 



SCHULZE-TIEMANN METHOD 



403 



centimeters of ferrous chlorid and two cubic centimeters of hydro- 
chloric acid are usually added. 

352. Measurement of the Gas.— The measurement of the gas 
was for some time conducted by the use of concentrated potash 
for absorbing the carbon dioxid, and ferrous chlorid for absorbing 
the nitric oxid. The use of the ferrous chlorid, however, was 
found to introduce a source of error. The treatment of the gas 
with oxygen and pyrogallol over potash has, therefore, been sub- 
stituted by Warington for absorption by ferrous chlorid. 

The chief source of error attending the oxygen process lies in 
the small quantity of carbon monoxid produced during the 
absorption with pyrogallol, but this error becomes negligible if the 
oxygen be only used in small excess. The amount of oxygen 
employed can be regulated by the use of Bischof's gas delivery 
tube. This may be made of a test-tube having a small perfora- 
tion half an inch from the mouth. The tube is partly filled with 
oxygen over mercury, and its mouth is then closed by a finely 
perforated stopper made from a piece of wide tube and fitted 
tightly into the test-tube by means of a covering of rubber. 
When this tube is inclined, the side perforation being down- 
wards, the oxygen is discharged in small bubbles from the per- 
forated stopper, while mercury enters through the opening. 
Using this tube, the supply of oxygen is perfectly under control 
and can be stopped as soon as a fresh bubble ceases to produce 
a red tinge on entering. Warington concludes his description 
by stating that in the reaction proposed by Schloesing the 
analyst has a means of determining a very small quantity of 
nitric acid with considerable accuracy, even in the presence of 
organic matter; but to accomplish this, the various simplifica- 
tions consisting in the omission of the stream of carbon dioxid, 
and the collection of the gas over caustic soda must be aban- 
doned, and special precautions must be taken to exclude all 
traces of oxygen from the apparatus. 

353- Schulze-Tiemann Method. — The modification of Schulze- 
Tiemann in the ferrous salt method consists chiefly in the omis- 
sion of the use of carbon dioxid, and in the simplified form of 
apparatus, which permits rapid work and gives, also, accord- 






404 



AGR1CUI.TURAI, ANALYSIS 



4 



ing to some authorities, very exact and reliable results.*- The 
extract, representing 500 grams of the fine soil, is reduced by evap- 
oration to 100 cubic centimeters and placed in a glass flask, A 
(Fig. 23), of 500 cubic centimeters capacity. The flask is closed 
with a rubber stopper, carrying two bent glass tubes which pass 
through it. The tube a b c is drawn out into a point at a and 
reaches about two centimeters below the surface of the rubber 
stopper. The tube e f g passes just to the lower surface of the 




Fig. 23. Schulze-Tiemann's Nitric Acid Apparatus. 

rubber stopper. The two tubes mentioned are .connected, by 
means of rubber tubes and pinch-cocks, with the tubes d and h. 
Ihe pmch-cocks at c and g must be capable of closing the tubes 
air-tight. The end of the tube g h passes into a crystallizing 
dish, B, and is bent upward to a point passing two to three cen- 
timeters into the measuring tube C. The point within the tube 
IS covered with a piece of rubber tubing. The measuring tube C 
IS divided into tenths of a cubic centimeter, and together with 
the crystallizing dish, B, is filled with a 10 per cent, solution of 
*'' Zeitschrift fiir analytische Chemie, 1870, 9 : 24, 401. 

Die landwirtschaftlichen Versuchs-Stationen, 1867, 9 : 9. 

Berichte der deutschen cheniischen Gesellschaft, 1873, 6 : 1038. 



SCHULZE-TIKMANN METHOD 



405 



I? 



boiled soda-lye, which is obtained by dissolving 12.9 parts of 
sodium hydroxid in 100 parts of water. 

The liquid which is to be examined for nitric acid (the pinch- 
cocks being opened and the tube g h not dipping into the crys- 
tallizing dish), is boiled for one hour in order to drive the air 
out of the flask A. The end of the tube e f g h is then brought 
into the crystallizing dish containing the sodium hydroxid solu- 
tion so that the steam escaping from the flask, A, escapes partly 
through the tube bed and partly through the tube f g h, not 
allowing, however, the bubbles to enter the measuring tube C. 
To determine whether the air is all expelled, the pinch-cock at g 
is closed and the soda-lye will thereupon rise to g in case no air 
interferes. It is best to close the tube at g first with the thumb 
and finger, and then the rise of the soda-lye to that point can be 
determined by the impulse felt. The tube is then firmly closed by 
means of the pinch-cock g. The rest of the steam is allowed 
to escape through the tube abed, and the evaporation is con- 
tinued until the contents of the flask are evaporated to about 10 
cubic centimeters. The flask into which the tube e d dips is 
filled with freshly boiled water. The lamp is removed from the 
flask A, the pinch-cock is closed, whereupon the tube e d be- 
comes filled with the freshly boiled water. The measuring tube, 
C, filled with freshly boiled soda-lye, is closed with the thumb 
and brought into the dish B, care being taken that no bubble 
of air enters. It is placed over the end of the tube g h. 

The pressure of the external air will now flatten the rubber 
tubes at e and g. The flask at the end of e d, holding freshly 
boiled water, is then replaced with one filled with a nearly satu- 
rated solution of ferrous chlorid containing some hydrochloric 
acid. The flask containing the ferrous chlorid solution should 
be graduated so that the amount which is sucked into the flask 
A can be determined. The pinch-cock e is opened and from 
15 to 20 cubic centimeters of the ferrous chlorid solution allowed 
to flow into A. The end of the tube e d is then placed in an- 
other flask containing strong hydrochloric acid, and the latter al- 
lowed to flow into the tube in small quantities at a time until 
all the ferrous chlorid is washed out of the tube bed into A. 



it! 



• r 

!>1 



,j » 

m 

S4 






:4. 






"if 1 



4o6 



AGRICULTURAL ANALYSIS 



At the point b there is sometimes formed a little bubble of hydro- 
chloric acid in the state of gas, which by heating the flask A 
completely disappears. 

The flask A is next warmed gently until the rubber tubes at 
the pinch-cocks begin to assume their normal condition. The 
pinch-cock at g is now replaced by the thumb and finger, and as 
soon as the pressure within the flask A is somewhat stronger, 
caused by the nitric oxid gas evolved from the mixture, it is 
allowed to pass through the tube e f g h and escape into the meas- 
uring cylinder C. By a manipulation of the finger and thumb 
at g, it is possible to prevent regurgitation of the sodium hydroxid 
into A, and at the same time to relieve the pressure of the nitric 
oxid in A, which would be difficult to do by means of the pinch- 
cock alone. 

The boiling of the liquid is continued until there is no longer 
any increase of the volume of gas in the measuring cylinder C. 
After the end of the operation the tube g h h removed from the 
clish B and the measuring tube C is closed by means of the 
thumb while its end is still beneath the surface of the soda-lye, 
and it is shaken until all traces of any hydrochloric acid which 
may have escaped absorption are removed. It is then placed 
in a large glass cylinder filled with water at the temperature 
at which the volume of gas is to be read. After being kept at 
this constant temperature for about half an hour the volume of 
the nitric oxid can be read. For this purpose the measuring 
cylinder C is sunk into the water of the large cylinder until 
the level of the liquids within and without the tube is the same. 
The usual correction for pressure of the atmosphere, as deter- 
mined by the barometer, and for the tension of the aqueous 
vapor at the temperature at which the reading is made, is ap- 
plied. The correction is made by means of the following formula : 

y. _ V X 273 X (B -/) 
(273 + O X 760 

In this formula V denotes the volume of the gas at the tem- 
perature of zero and at 760 millimeters barometric pressure; V, 
the volume of the gas as read at the barometric pressure observed, 



Spiegel's modification 



407 



B, and the temperature observed, t, while / denotes the tension 
of the aqueous vapor in millimeters of mercury pressure at the 
observed temperature, t. The tension of the aqueous vapor at 
temperatures from zero to 26°, expressed in millimeters of mer- 
cury, is given in the following table: 



Temp. 


Tension in mm. 


Temp. 


Tension in mm. 


Temp. 


Tension in mm 





mercury. 





mercury. 





mercury. 





4.6 


9 


8.5 


18 


15.3 


I 


4-9 * 


10 


9.1 


19 


16.3 


2 


5-3 


II 


9-7 


20 


17.4 


3 


5.7 


12 


10.4 


21 


18.5 


4 


6.1 


13 


II. I 


22 


. 19.6 


5 


6.5 


14 


11.9 


23 


20.9 


6 


6.9 


15 


12.7 


24 


22.2 


7 


7-4 


16 


13.5 


n 


23-5 


8 


8.0 


17 


14.4 


26 


25.0 



From the gas volume corrected by the above formula the nitric 
acid is calculated as follows : 

One cubic centimeter of nitric oxid weighs at 0° and 760 milli- 
meters barometric pressure 1.343 milligrams. 

Since two molecules of NO (molecular weight 60) correspond 
to one molecule of N2O5 (108), we have the following equa- 
tion: 60 : 108= 1.343 :x. Whence x = 2.417 milligrams, the 
weight of nitric acid (N2O5) corresponding to one cubic centi- 
meter of nitric oxid. 

354. Spiegel's Modification. — Spiegel noticed inaccuracies in 
the results of the ferrous chlorid method of estimating nitric acid 
when carbon dioxid is used, which sometime^ amounted to three 
per cent, of the nitric acid present in the sample. The following 
suggestions are made by him for the improvement of the pro- 
cess r"*^ 

As regards the use of carbon dioxid in the operation, the first 
difficulty consists in obtaining it entirely free from air. By the 
use of small pieces of marble, which, before being placed in the 
kipp apparatus are kept for a long while in boiling water, a pro- 
duct is obtained which, after 30 minutes of moderate evolution, 
leaves only a trace of unabsorbed gas in contact with potash-lye. 
The apparatus used is illustrated in Fig. 24. . 

** Berichte der deutschen chemischen Gesellschaft, 1890^ 23 : 1361. 



I I 



t! 4. 



4o8 



AGRICUI.TURAI, ANAI^YSIS 



A is a round flask of about 150 cubic centimeters capacity, 
furnished with a well-fitting rubber stopper provided with two 
holes, one for the entrance of the funnel tube B and the other 
for the delivery tube C. The tube B ends about two centimeters 
above the bottom of A and carries a bulb-shaped funnel at its top 
capable of holding about 50 cubic centimeters. The gas tube 
D is ground into the bulb of B as shown in the figure. 

After the flask has been filled with the solution to be ex- 




Fig. 24. Spiegel's Apparatus for Nitric Acid. 

amined, carbon dioxid is conducted through D and the flask 
is heated to boiling until the gas which escapes through C no 
longer contains any air. The measuring tube is brought over 
the end of the delivery tube C, in the usual manner ; but is not 
shown in the figure, in the funnel of B are placed 20 cubic 
centimeters of previously prepared and boiled ferrous chlorid 
solution and this liquid is allowed to flow partly into A by lift- 



Dt konnick's modip^ication op^ schloksing's method 409 

ing slightly the gas-tube D. About 40 cubic centimeters of 
concentrated, boiled hydrochloric acid are afterwards added to it 
in the same way. As soon as the liquid in the flask A is again 
boiling, the stream of carbon dioxid is shut off and allowed to 
flow again only towards the end of the operation, when the con- 
tents of the flask are reduced almost to dryness. As will be 
seen from the above directions, no unboiled liquids of any kind 
are to be used as reagents in the apparatus described. If the 




H 



Fig. 25. De Konnick's Apparatus. 

flask A were made much smaller the efliciency of this apparatus 
would be increased. It appears to have few, if any, advantages 
over Warington's process. 

355- De Konnick's Modification of Schloesing's Method. — This 
modification consists in an arrangement of the gas delivery tube, 
whereby the regurgitation of the water in the measuring burette 
i"to the evolution flask is prevented by a device for sealing the 



1" 

V 









4IO 



AGRICULTURAL ANALYSIS 



delivery tube with mercury.** The apparatus is arranged as 
shown in Fig. 25. The flask in which the decomposition takes 
place is provided with a long neck, into which a side tube is 
sealed and bent upwards, carrying a small funnel attached to it 
by rubber tubing. The piece of rubber tubing carries a pinch- 
cock, by means of which the solution containing the nitrate and 
hydrochloric acid can be introduced into the flask. The small 
gas delivery tube is arranged as shown in the figure, and carries 
at the end next the burette a device shown in Fig. 26. The cork 
represented in this device has radial notches cut in it, so as to 
permit of a free communication between the water in the burette 
and in the pneumatic trough. The open end of the burette, when 
the apparatus is mounted ready for use, rests on the notched sur- 




Fig. 26. End of Delivery Tube. 

face of the cork, and the end of the delivery tube is placed in the 
crystallizing dish resting on the bottom of the pneumatic trough. 

The end of the delivery tube, as indicated, has fused to it a 
vertical tube, open at both ends and from six to seven centimeters 
in length, and carrying the notched cork already described. The 
crystallizing dish in the bottom of the pneumatic trough is filled 
with mercury until the point of union of the delivery tube with 
the vertical end is sealed to the depth of a few millimeters. As 
the gas is evolved it bubbles up through the mercury into the 
measuring tube and the displaced water passes out through the 
notches in the cork. Should any back pressure supervene, the 
mercury at once rises in the delivery tube, which is of such a 
length as to prevent its entrance into the flask. The operation 
can then be carried on with absolute safety. 

To make an estimation, there arc placed in the flask about 

** Zeitscbrift fiir analytische Chemie, 1894, 33 : 200. 



SCHMIDT S PROCESS 



411 



40 cubic centimeters of ferrous chlorid solution containing about 
200 grams of iron to the liter, and also an equal volume of hydro- 
chloric acid of I.I specific gravity. The side tube is also filled 
up to the funnel with the acid. The contents of the flask are 
boiled until all air is expelled, which can be determined by hold- 
ing a test-tube filled with water over the end of the delivery 
tube. The solution containing the nitrate is next placed in the 
funnel, the pinch-cock opened and the liquid allowed to run into 
the flask by means of the partial vacuum produced by stopping 
the boiling and allowing the mercury to rise in the delivery tube. 
All the solution is washed into the flask by successive rinsings 
of the funnel with hydrochloric acid, being careful to allow no 
bubble of air to enter. The contents of the flask are again 
raised to the boiling-point and the nitric oxid evolved collected in 
the nitrometer. The solution examined should contain enough 
nitrate to afford from 60 to 80 cubic centimeters of gas. With- 
out refilling the flask, from eight to nine determinations can be 
made by regenerating the ferrous chlorid by treatment with zinc 
chlorid. Care must be exercised not to add the zinc chlorid in 
excess, otherwise ammonia and not nitric oxid will be produced. 
The side tube and funnel must also be carefully freed from zinc 
chlorid by washing with hydrochloric acid. 

356. Schmidt's Process. — In the case of a water, or the aque- 
ous extract of a soil, according to the content of nitric acid, 
from 50 to 100 cubic centimeters are evaporated to 30 cubic cen- 
timeters, and the residue sucked into the generating flask of the 
apparatus. Fig. 2J, and, with the rinsings with distilled water, 
evaporated again to from 20 to 30 cubic centimeters, and the flask 
then connected, as shown in the figure, to a schiff measuring 
apparatus B.*^ This apparatus is previously filled to i with mer- 
cury, and the bulb g connected with ^ by a rubber tube. 

The apparatus is then filled with a 20 per cent, caustic soda 
solution previously boiled and still warm, until the bulb g is 
partially filled when raised a little above the cock h. Then h is 
closed and g held, by an appropriate support, on about the 
same level with h. The cock at b is then closed and e opened. 

^'^ Apotheker Zeitung, 1890, 5 : 287. 



ii 



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M 

A, i 









hf 



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{ 1 



1 



412 



AGRICULTURAL ANALYSIS 



Meanwhile the ebulHtion in the flask is continued, and the air 
bubbles rising in the schiff apparatus are removed, from time to 
time, by carefully opening h and raising g. When bubbles no 
longer come over, the cock at e is closed and at b opened, and 
the steam issuing at a is conducted through a mixture of ferrous 
chlorid and strong hydrochloric acid to free it, as far as possible, 
from air. When the contents of the flask have been evaporated 




Fig. 27. Schmidt's Apparatus. 

to about five cubic centimeters, h is closed and the lamp at once 
removed. 

By carefully opening h about 10 cubic centimeters of a mix- 
ture of ferrous chlorid and hydrochloric acid are allowed to enter 
the flask, when h is closed and the flask slowly heated until the 
positive pressure is restored. The pinch-cock c is then opened 
and the contents of the flask evaporated nearly to dryness. The 
cock e is again closed and the flame removed. Another quan- 
tity (15 cubic centimeters) of ferrous chlorid and hydrochloric 
acid solution is sucked into the flask and the process of distilla- 
tion repeated, whereby the whole of the nitric oxid is collected 



I 



MERCURY AND SULFURIC ACID METHOD 



413 



m 



in h. The nitric oxid evolved is measured in the usual way and 
calculated to nitric acid, one cubic centimeter of nitrogen dioxid 
being equal to 2.417 milligrams of nitric acid. 

357. Merits of the Ferrous Chlorid Process.— The possibility 
of an accurate determination of nitrates, by decomposition with 
a ferrous salt in presence of an excess of hydrochloric acid, has 
been established by many years of experience and by the testi- 
mony of many analysts. The method is applicable especially 
where the quantity of nitrate is not too small and when organic 
matter is present. In the case of minute quantities of nitrate, 
however, the process is inapplicable and must give way to some 
of the colorimetric methods to be hereafter described. 

In respect of the apparatus, modern practice has led to the 
preference of that form which does not require the use of carbon 
dioxid for displacing the air. Steam appears to be quite as ef- 
fective as carbon dioxid and is much more easily employed. That 
form of apparatus should be used which is the simplest in con- 
struction and has the least cubical content. 

The measurement of the evolved gas is most simply made by 
collecting over lye in an azotometer, reading the volume, noting* 
the reading of the barometer and thermometer and then reducing 
to standard conditions of pressure and temperature by the cus- 
tomary calculations. Where a very strong lye is used the ten- 
sion of the aqueous vapor may be neglected. While every analyst 
should have a thorough knowledge of the ferrous chlorid method 
and the principles on w^hich it is based, it can not be compared 
in simplicity to the later methods with ])ure nitrates, which are 
based on the conversion of the nitric acid into ammonia by the 
action of nascent hydrogen. In accuracy, moreover, it does not 
appear to have any marked advantage over the reduction methods. 

358. Mercury and Sulfuric Acid Method. — This simple and ac- 
curate method of determining nitric acid in the absence of organic 
matter is known as the Crum-Frankland process.'*" 

The method rests on the principle of converting nitric acid into 

^^ Philosophical Magazine, 1847, [3], 30 : 426. 
Journal of the Chemical Society, 1868, 21 : loi. 
Sutton, Volumetric Analysis, 9th Edition, 1907 : 443. ' 









i 









I 






^1 









I 



414 



AGRICULTURAL ANALYSIS 



nitric oxid by the action of mercury in the presence of sulfuric 
acid. The operation as at first described is conducted in a glass 
jar eight inches long by one and a half inches in diameter, filled 
with mercury and inverted in a trough containing the same liquid. 
The nitrate to be examined, in a solid form, is passed into the 
tube, together with three cubic centimeters of water and five of 
sulfuric acid. With occasional shaking, two hours are allowed 
for the disengagement of the gas, which is then measured. 

359. Warington's Modification. — A graduated shaking-tube is 
employed, which allows the nitrate solution and oil of vitriol to 
be brought to a definite volume.*^ The nitrate solution, with rms- 
ings, is always two cubic centimeters, and enough sulfuric acid 
is added to increase the volume to five cubic centimeters. The 
sulfuric acid should give no gas when shaken with distilled water. 
Any gas given off in the apparatus before shaking is not expelled 
but is included in the final result. The persistent froth some- 
times noticed where some kinds of organic matter are present, 
is reduced by the addition of a few drops of hot water through 
the stop-cock of the apparatus. The nitric oxid is finally meas- 
ured in Frankland's modification of Regnault's apparatus. 

This method, accurate for pure nitrates, unfortunately fails in 
the presence of any considerable amount of organic matter. 

According to Warington's observations, the presence of chlo- 
rids is no hindrance to the accurate determination of both nitric 
and nitrous acids by the mercury method. This simplifies the 
operation as carried on by Frankland, who directs that any chlorin 
present be removed before the determination of the nitric acid is 
commenced. 

360. Noyes' Method. — In the analyses made by Noyes for 

the National Board of Health, the Crum-Frankland method was 

employed."*^ The apparatus used was essentially that w^hich is 

now known as Lunge's nitrometer, and it will be described in 

the next paragraph. No correction is made by Noyes for the 

tension of aqueous vapor in the measurement of the nitric oxid 

because of the moderate dilution of the sulfuric acid by the liquid 

*'' Journal of the Chemical Society, 1879, 35 : 376. 
*^ Report of the National Board of Health, 1882 : 281. 



i 



lunge's nitrometer 



415 



holding the nitric compounds in solution. The chlorin is not re- 
moved from the dry residue of the evaporated water, as its pres- 
ence in moderate quantity does not interfere with the accuracy 
of the process. In order to obtain the amount of nitrogen in the 
form of nitrates, the total volume of nitric oxid must be dimin- 
ished by that due to nitrites present, which must be determined in 
a separate analysis. The method of manipulation is given in the 
following paragraph. 

361. Lunge's Nitrometer. — The apparatus employed by Noyes, 
in a somewhat more elaborate form, is known as Lunge's nitrom- 
eter.*^ This apparatus is shown in Fig. 28. It consists of a 




Fig. 28, Lunge'.s Nitrometer. 

burette a, divided into one-fifth cubic centimeters. At its upper 
end it is expanded into a cup-shaped funnel attached by a three- 
way glass stop-cock. Below, the burette is joined to a plain tube 
b, of similar size, by means of rubber tubing. The apparatus is 
first filled with mercury through the tube b, the stop-cock being 
so adjusted as to allow the mercury to fill the cup at the top of a. 
The cock is then turned until the mercury in the cup flows out 
*® Berichte der deutschen chemischen Gesellschaft, 1878, 11 : 437. 



f 



I! 



I >i 



it' 






I 



416 



AGRICULTURAIv ANALYSIS 



through the side tube, carrying the rubber tube and clamp. The 
three-way cock is closed, and the solution containing the nitrate 
placed in the cup. By lowering the tube b and opening the cock 
the liquid is carefully passed into a, being careful to close the 
cock before all the liquid has passed out of the cup. By repeated 
rinsings with pure concentrated sulfuric acid, every particle of the 
nitric compound is finally introduced into a, together with a large 
excess of sulfuric acid. The total volume of the introduced liquid 
should not exceed 10 cubic centimeters. The mixture of the mer- 
cury, nitric compound, and sulfuric acid is effected by detaching 
a from its support, compressing the rubber connection between a 
and b, placing a nearly in a horizontal position, and quickly bring- 
ing it into a vertical position with vigorous shaking. 

After about five minutes the reaction is complete, and the level 
of the liquids in the two tubes is so adjusted as to compensate 
for the difference in specific gravity between the acid mixture in 
a and the mercury in ^ ; in other words, the mercury column in b 
should stand above the mercury column in a one-seventh of the 
length of the acid mixture in a. This secures atmospheric pres- 
sure on the nitric oxid which has been collected in a. The meas- 
ured volume of nitric oxid should be reduced to 0° and 760 milli- 
meters barometric pressure. Each cubic centimeter of nitric oxid 
thus obtained corresponds to 1.343 milligrams NO; 2.417 milli- 
grams N2O5; 1.701 milligrams N2O3 ; 2.820 milligrams UNO.,; 
4.521 milligrams KNO^, and 3.805 milligrams NaNOg. 

362. Lunge's Improved Apparatus. — Lunge has improved his 
apparatus for generating and measuring gases and extended its 
applicability.^^ The part of it designed to measure the volume of 
a gas is the same in all cases. For generating the gas, the ap- 
paratus varies according to the character of the substance under 
examination. 

The measuring apparatus is shown in Fig. 29. It is composed 
essentially of three tubes, conveniently mounted on a wooden 
holder with a box base for saving any spilled mercury. The 
support is not shown in the illustration. 

The tubes A, B, C, are mutually connected by means of a 

^ Bulletin de la Soci^t^; chiuiique de Paris, 1894, [3], 11 : 625. 



LUNGE S IMPROVED APPARATUS 



417 



three-way tube and rubber tubing, w^ith very thick walls to safely 
hold the mercury without expansion. In the middle of the meas- 
uring tube A is a bulb of 70 cubic centimeters capacity. Above 
and below the bulb the tube is divided into tenths of a cubic cen- 
timeter, and its diameter is such, viz., 11.3 millimeters, that each 
cubic centimeter occupies a length of one centimeter. The upper 

d 






Fig. 29. lyunge's Improved Apparatus. 

end of A is closed with a glass cock with two oblique perforations, 
by means of which communication can be established at will, 
either through e with the apparatus for generating the gas, or 
through dy with the absorption apparatus, or the opening be com- 
pletely closed. 

The volume of air under the observed conditions, which would 
14 



i 



4} 






t,' 



t 



'If* 



: I 'i 



418 



AGRICULTURAL ANALYSIS 



measure exactly 100 cubic centimeters at 0° and 760 millimeters 
pressure of mercury, is calculated by the formula 

^ 100 (273 + 760 
273 (H) 
where / equals observed temperature, b the barometric pressure 
less the correction noted below, and / the tension of the vapor of 
water under existing conditions. For example: 

Temperature 18° 

Barometric reading 755 

Correction for d 2 

Corrected barometer 753 

Vapor of water tension 16 

^1.ot. \T 100(273+ 18) 760 

Ihen V = ; -^ — = 109.9. 

273 (753—16) 

This indicates that 109.9 cubic centimeters of air would occupy 
a volume of 100 cubic centimeters when subjected to standard 
conditions. 

The tubes A, B, and C, are filled with mercury of which about 
two and a half kilograms w^ill be required. By means of the 
leveling tube B, the stopper in C being opened, the mercury in 
C is brought exactly to 109.9 ctibic centimeters. The stopper 
in C is then closed, mercury poured into D, which is then closed 
with a rubber stopper, carrying a small glass tube, as indicated 
in the figure. 

The leveling tube B serves to regulate the pressure on the 
gas in A, and this is secured by depressing or elevating it, as the 
case may require. 

The tube for reducing the volume to standard conditions of 
temperature and pressure, viz., 0° and 760 millimeters of mer- 
cury, is shown in C. In its narrow part, which has the same in- 
ternal diameter as A, it is graduated into tenths of a cubic centi- 
meter. The upper end of C is furnished with a heavy glass neck 
D, surmounted by a glass cup. In the neck is placed a ground- 
glass stopper, carrying a groove below, which corresponds to a 
similar groove above in the side of the neck, whereby communica- 
tion can be established at will between the interior of C and the 
exterior. The joint is also sealed by pouring mercury into D, as 



METHOD OF MANIPULATION 



419. 



is shown in the figure. When the stopper is well ground and! 
greased the reduction tube may be raised or lowered as much as 
may be necessary without any danger of escape or entrance o£ 
gas. To determine the position of the reduction tube C the 
reading of the barometer and thermometer at room temperature 
is taken. From the reading of the barometer subtract one milli- 
meter if the temperature be below 12°, two millimeters at a 
temperature from 12° to 19°, three from 20° to 25°, and four 
above 25°. 

When a gas has been introduced into the measuring tube A 
it is brought to the volume which it would assume under stand- 
ard conditions by adjusting the tube C, in such a way as to bring 
the mercury in C and A to the same height and the surface 
of the mercury in C is exactly at 100 cubic centimeters. The 
gas in A is then at the volume which it would occupy under 
standard conditions, and this volume can be directly read. This- 
adjustment is secured by moving the tubes B and C up or down. 
If gases are to be measured wet, a drop of water should be put 
on the side of the upper part of C, and if dry, of sulfuric acid^ 
before the adjustment for temperature and pressure. 

363. Method of Manipulation. — By the action of mercury ins 
the presence of sulfuric acid, the nitrogen in nitrates, nitrites, 
nitrosulfates, nitroses, nitrocellulose, nitroglycerol, and the greater 
number of explosives, may be obtained and measured as nitric 
oxid. The nitrogen compounds are decomposed in the apparatus 
shown in Fig. 30. 

To make an analysis, the apparatus is filled with mercury, 
through F, until the two openings in the cock and / are entirely 
occupied with that liquid. The cock li is then closed, and the 
nitrogen compound, in solution, introduced through g, care being 
taken that no air enters g when F is depressed and h opened to 
admit the sample. The funnel g is washed several times with a 
few drops of sulfuric acid, which are successively introduced inta 
G. The total liquid introduced should not exceed 10 or 15 cubic 
centimeters, of which the greater part should be sulfuric acid. 
The rubber tube connecting G and F is carefully closed with a 
clamp and G violently shaken for a few minutes until no further 






i>'t 



«f, 



4 









m 
l^ 



\% 






* 



420 



AGRICULTURAL ANALYSIS 



evolution of nitric oxid takes place. In shaking, the apparatus 
should be so held as to prevent the escape of the mercury from 
the small tube i by keeping it closed v/ith the finger or drawmi; 
over it a rubber cap. 

After the evolution of the gas has ceased, the tube e, Fig. 29, 
is brought into contact with i, (Fig. 30) and the two are joined 
by a tight-fitting piece of rubber tubing in such a way as to ex- 
clude any particle of air. The tube F, Fig. 30, is lifted and B 
and C, Fig. 29, depressed. On carefully opening the cocks h and 
b, and bringing i and e into union, the gas is passed from G into 
A. When all the gas-^s entered A and the acid mixture from 




Fig. 30. Lunge's Analytic Apparatus. 

G has reached b, the latter is closed, and also h. The apparatus 
G is disconnected and removed. The gas in A is then reduced to 
normal conditions by manipulating the reduction tube, C, in the 
manner already described. 

The gas in A is measured dry by reason of having been gen- 
erated in presence of rather strong sulfuric acid. Consequently, 
for this operation the adjustment of the volume of gas in C 
should be made in contact with a drop of strong sulfuric acid. 
In order to make the readings, a quantity of material must be 



VOLUMLTRIC METHOD OF GANTTER 



421 



taken which will give not less than 30 and not more than 140 
cubic centimeters of nitric oxid. 

The quantities of the difTerent compounds of nitric acid cor- 
responding to the number of cubic centimeters of nitric oxid, 
measured under standard conditions, are shown in the following 
table : 

Corresponding to 

/ — * , 

Cubic centimeters Weight in N0O3 in HNO3 in NaNOa in 

of NO. milligrams. milligrams. milligrams. milligrams. 

I 1.343 1. 701 2.820 3.805 

2 2.682 3.402 5.640 7.610 

3 4.029 5.103 8.460 11.415 

4 5-372 6.804 11.280 15.220 

5 6.715 8.506 14.100 19.025 

6 8.058 10.206 16.920 22.830 

7 9-40I 11.907 19.740 26.635 

8 10.744 13.608 '• ' 22.560 30.440 

9 12.087 15-309 25.380 34-245 

364. Utility of the Method. — Where it is desirable that the 
nitric oxid method be used, and at the same time heating be 
avoided, the decomposition of a nitrate by means of metallic 
mercury and sulfuric acid affords a convenient and accurate pro- 
cedure. But, as a rule, there is no objection to the application 
of the lamp except in the case of explosives, and in such cases the 
mercury method appears to have no advantage over the ferrous 
chlorid process. Nevertheless, in the hands of- a skilled worker, 
the results are reliable, and the process is a quicker one, on the 
whole, than by distillation with ferrous chlorid and hydrochloric 
acid. 

365. Volumetric Method of Gantter. — The process proposed 
by Gantter for determining the nitrogen volumetrically in Chile 
saltpeter and other nitrates is based on the following principles :°^ 

(1) If a nitrate be heated in contact with sulfuric and phos- 
phorous acids, nitrous and phosphoric acids will be formed. 

(2) If nitrous acid be boiled with ammonium chlorid, nitrogen 
will be quantitatively evolved from both compounds. These pro- 
cesses are illustrated by the following formulas: 

(a) N,0,+P,03=N,03+PAv 

(b) N^Oa-f 2NH,Cl=2No+3HoO+2HCl. 

^^ Zeitschrift fiir analytische Cheiuie, 1895, 34 : 26. 



in 

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1** 
Us 






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422 



AGRICULTURAL ANALYSIS 



It is seen from the above that the nitrate will give, by this 
treatment, double the volume of nitrogen which it contains. In 
practice, the two reactions may be secured in one operation by 
warming the nitrate solution slowly with sulfuric and phos- 
phorous acids and ammonium chlorid. The nitric acid, as it be- 
comes free, gives a part of its oxygen to the phosphorous com- 
pound, and the nitrous acid, in a nascent state, is at once reduced 
by the ammonium chlorid. There are two sources of error which 
must be guarded against in the work ; a portion of the nitrogen 
may escape reduction to the elementary state, or some of the 
nitrate may fail to be decomposed. These errors are easily 




<f'' 




Fig. 31. Gantter's Nitrogen Apparatus. 

avoided if the reaction be begun slowly, so that the evolution of 
gas may be gradual. The temperatures at first should, therefore, 
be kept as low as possible. The development of red fumes, show- 
ing the presence of undecomposed nitrogen oxids, shows that 
the results will be too low. It is necessary, also, to provide for 
the absorption of the hydrochloric acid which is formed. The 
reaction is very conveniently conducted in the apparatus shown 
in Fig. 31. The decomposition takes place in the flask A, and 
the mixed gases pass into the absorption bulb C. The delivery 
tube is very much expanded, as shown in the figure, so that no 
soda-lye can enter A durinrr the cooling of the flask. The absorp- 



I 



n 



VOLUMETRIC METHOD OF GANTTER 



423 



tion bulb is connected with A and B by the tubes a and b, as 
shown. The tube d connects the apparatus with the gasvolu- 
meter.^^ The bulb B serves as a pipette for the introduction 
of the decomposing acid. The operation is conducted as follows : 
Three cubic centimeters of the nitrate solution, containing no 
more than 300 milligrams of the substance, are placed in the 
flask A, with half a gram each of crystallized ammonium chlorid 
and phosphorous acid. In the bulb B ai e placed seven cubic cen- 
timeters of sulfuric acid, to which has been added one-third its 
volume of water. Two cubic centimeters of acid are allowed to 
flow from B into A. The apparatus is brought to a constant 
temperature by being immersed in a large cylinder E, containing 
water at a temperature which can easily be controlled. When 
this constant temperature has been reached the apparatus is taken 
from the cooling cylinder, which contains also a smaller cylinder 
D, nearly filled with water and connected through f with the 
measuring apparatus M. The barometer-tube F is half filled 
with colored water, so that the pressure may be equalized before 
and after the operation. The flask A is warmed very gently at 
first, and the nitrogen evolved is conducted into D, driving an 
equivalent volume of water into M. The evolution of the gas 
must be carefully controlled and the heat at once removed if it 
becomes too rapid. The appearance of a red color shows the 
evolution of oxids of nitrogen, rendering the analysis inexact. 
When the evolution of nitrogen has nearly ceased, the lamp is 
removed and some more sulfuric acid allowed to flow into A 
from B, after which A is again heated, this time to the boiling- 
point. All vapors of hydrochloric acid produced are absorbed 
by the soda-lye in C. The boiling is continued a few minutes, 
but not long enough to darken the liquid in A. After replacing the 
apparatus in the cylinder E, and bringing both temperature and 
pressure to the same point as before the beginning of the opera- 
tion, the volume of nitrogen evolved is determined by measuring 
the water in M. 

The apparatus is first set by using pure potassium or sodium 
nitrate. Since the temperature and pressure do not vary much 

^' Zeitschrift fiir analytische Cheniie, 1893, 32 : 553- 






;:? 



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II 






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424 



AGRICULTURAL, ANALYSIS 



within an hour or two, the volume of water obtained with a sam- 
ple of Chile saltpeter can be compared directly with that given 
off by the same weight of a pure potassium or sodium nitrate 
without correction. 

Example. — Two hundred and fifty milligrams of potassium 
nitrate, containing 34.625 milligrams of nitrogen, displaced in a 
given case 60 cubic centimeters of water : therefore, one cubic 
centimeter of water equals 0.578 milligram of nitrogen. If 289 
instead of 250 milligrams be taken, then the number of cubic cen- 
timeters of water displaced divided by five will give the per cent, 
of nitrogen. 

366. Method of Difference. — In the analysis of Chile salt- 
peter by the direct method a variation of 0.25 per cent, in the 
content of nitrogen is allowed from the dealers' guaranty. This 
would allow a total variation in the content of sodium nitrate 
of 1.52 per cent. Dealers and shippers have always been accus- 
tomed to estimate the quantity of sodium nitrate in a sample by 
difference ; i. e., by estimating the constituents not sodium nitrate 
and subtracting the sum of the results from 100. Chile saltpeter 
usually contains sodium nitrate, water, insoluble ferruginous mat- 
ters, sodium chlorid, sodium sulfate, magnesium chlorid, sodium 
iodate, calcium sulfate and sometimes small quantities of potas- 
sium nitrate. 

When the total sodium nitrate is to be estimated by difference, 
the following procedure, suggested by Crispo, may be followed :^^ 

Water. — Dry 10 grams of the finely powdered sample to con- 
stant weight at i50°-i6o°. 

Chlorin. — The residue, after drying, is dissolved and the vol- 
ume made up to one-fourth liter with water and the chlorin de- 
termined in one-fifth thereof and calculated as sodium chlorid. 

Insoluble. — Twenty grams are treated with water until all solu- 
ble matter has disappeared, filtered on a tared gooch, and the 
crucible dried to constant weight. 

Sulfuric Acid. — The sulfuric acid is precipitated by barium 
chlorid in the slightly acid filtrate from the insoluble matter. 
5' L'Engrais, 1894, 9 : 877. 



i \ 



principle:s of the method 



425 



The acidity is produced by a few drops of nitric acid. The rest 
of the process is conducted in the usual way. 

Magnesia. — This is precipitated by ammonium sodium phos- 
phate, filtered, ignited, and weighed as pyrophosphate. The mag- 
nesia is then calculated as chlorid. Magnesia is rarely found 
in excess of one-fourth per cent. When this amount is not ex- 
ceeded the estimation of it may be neglected without any great 
error. As has already been said, the chlorin is all calculated as 
sodium chlorid. If a part of it be combined wdth one-fourth 
per cent, of magnesia, it would represent 0.59 per cent, of mag- 
nesium chlorid instead of 0.73 per cent, sodium chlorid. In 
omitting the estimation of the magnesia, therefore, the importer 
is only damaged to the extent of 0.14 per cent, of sodium nitrate. 

Sodium Iodate. — This body, present only in small quantities, 
may also be neglected. In case the content of this body should 
reach one-fourth per cent, the estimation of chlorin by titration, 
using potassium chromate as indicator, is impracticable. Such an 
instance, however, is rarely known. 

Approximate Results. — When the determinations outlined above 
have been carefully made, it is claimed that the result obtained 
by subtraction from 100 will not vary more than from two-tenths 
to three-tenths per cent, from the true content of sodium nitrate. 
The method, however, cannot be considered strictly scientific and 
is much more tedious and chronophagous than the direct deter- 
mination. In the direct determination, however, the analyst must 
assure himself that potassium is present in only appreciable quan- 
tities, otherwise the per cent, of sodium nitrate will be too low. 

The presence of potassium nitrate is a detriment in this re- 
spect only ; viz., that it contains a less percentage of nitrogen 
than the corresponding sodium salt. As a fertilizer, the value 
•of Chile saltpeter may be increased by its content of potassium, 

ESTIMATION OF NITRIC ACID BY OXIDATION OF A 

COLORED SOLUTION 

367. Principles of the Method.— Solutions of organic coloring 
matter in certain conditions are decolorized by nitric acid. The 
process is one of oxidation and the disappearance of the natural 






I 






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426 



AGRICUI.TURAL ANAI^YSIS 



color marks the end of the reaction. Indigo is the only coloring 
matter that has been used to any extent in this process. 

368. Method of Marx.— The indigo method as usually practiced 
is conducted according to the principle described by Marx.^* 
There are required for the process the following reagents and 
apparatus : 

a. A solution of pure potassium nitrate containing 1.8724 grams 
per liter. One cubic centimeter of the solution is equivalent to one 
milligram of nitric anhydrid (N2OJ. 

b. A solution of the best indigo carmine in water, which should 
be approximately standardized by solution in the manner described 
hereafter, and then diluted so that from six to eight cubic centi- 
meters equal one milligram of nitric acid. 

c. Chemically pure sulfuric acid of specific gravity 1.842, per- 
fectly free from sulfurous and arsenious acids and nitrogen oxids. 

d. Several thin flasks of about 200 cubic centimeters capacity. 

e. A small cylindrical measure holding 50 cubic centimeters 
and divided into cubic centimeters. 

/. A Mohr's burette divided into tenths of a cubic centimeter. 

g. A 25 cubic centimeter pipette or another burette. 

h. A hvQ cubic centimeter pipette divided into cubic centime- 
ters or half cubic centimeters. 

i. A measuring flask of 250 cubic centimeters capacity. 

Preliminary TWa/.— Twenty-five cubic centimeters of the sam- 
ple are transferred to a flask; the 50 cubic centimeter measure 
IS filled with sulfuric acid and the burette with indigo solution 
Ihe sulfuric acid is added to the sample all at once,- shaken for 
a moment, and the indigo run in as quickly as possible with 
shaking until a permanent greenish tint is produced. If the 
sample does not require more than 20 cubic centimeters of indigo 
solution of the above strength, it can be titrated directly other- 
wise It must be diluted with a proper quantity of pure water, 
and subjected again to the preliminary trial. 

The Actual Titration.-(i) Twenty-five cubic centimeters of 
the sample, properly diluted if necessary, are poured into a flask, 
and as much indigo as was used in the preliminary trial is added; 

^ Zeitschrift fiir analytische Chemie, 1868, 7 : 412. 






A 



METHOD OF BOUSSINGAULT 



427 



a quantity of sulfuric acid, equal in volume to the liquid in the 
flask, is added all at once, the mixture shaken, and indigo solu- 
tion run in quickly out of the burette until the liquid remains per- 
manently of a greenish tint. 

(2) The last experiment is repeated as often as may be neces- 
sary, adding to the water at first half a cubic centimeter less 
indigo than the total quantity used previously, afterwards pro- 
ceeding as in ( I ) until the final test shows too little indigo used. 

(3) From the rough titration of the indigo, calculate the 
amount of potassium nitrate solution corresponding with the in- 
digo solution used in (2), multiply the result by 10, transfer this 
quantity of the standard nitrate solution to a 250 cubic centime- 
ter flask, fill with pure water to the mark, and titrate 25 cubic 
centimeters of this fluid with indigo as in (2). If the quantity 
of indigo solution used is nearly the same as that required in (2), 
its exact value may be calculated, but if it is not, another nitrate 
solution may be made up in the 250 cubic centimeter flask, more 
closely resembling the sample in strength, and the titration with 
the indigo solution must be repeated. 

(4) If the water contains any considerable amount of organic 
matter, it must first be destroyed by potassium permanganate. 
In this case, the estimation of the organic matter and nitric acid 
may be conveniently combined. 

The use of permanganate in the above case is likely to intro- 
duce an error as has been shown by Warington. The method, 
therefore, can not be recommended in the presence of organic 
matter. 

369. Method of Boussingault.— The process for the estima- 
tion of nitric acid by the decoloration of a solution of indigo is 
due originally to Boussingault." In this method the extract, ob- 
tained by washing slowly 200 grams of soil until the filtrate 
amounts to 300 cubic centimeters, is evaporated until its volume 
is no greater than two or three cubic centimeters, and it is trans- 
ferred to a test-tube, with washings, and again evaporated in the 
tube until the volume is not greater than that last mentioned. A 
few drops of solution of indigo are added, and then two cubic 
^ Encyclopddie chimi(|ue, 1888, 4 : i54. 



,i 









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4V 



i 



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I 



428 



AGRICULTURAL ANALYvSiS 



centimeters of pure hydrochloric acid; the whole is then heated. 
As the color of the indigo disappears more is added. When the 
color ceases to fade, the liquid in the test-tube is concentrated 
by boiling. If concentration fail to destroy the blue or green 
color, another one-half cubic centimeter of hydrochloric acid is 
introduced. The reaction is completed when neither concentra- 
tion nor fresh addition of hydrochloric acid destroys the excess 
of indigo present. The color produced by a small excess of in- 
digo is a bright green ; this tint is the final reaction sought. The 
small excess of indigo necessary to produce a green color is de- 
ducted in every experiment. 

When more than mere traces of organic matter are present, 
Boussingault advises that the nitric acid be first separated by 
distillation and then reduced by the indigo solution. For this 
purpose the concentrated solution of the nitrate, two or three 
cubic centimeters, is placed in a small tubulated retort with two 
grams of manganese dioxid in fine powder. The retort is next 
half filled with fragments of broken glass, over which is poured 
one cubic centimeter of concentrated sulfuric acid. The retort 
is heated carefully by means of a small flame, which is kept in 
motion so as to successivelv come in contact with all parts of 
the bottom of the retort. The distillate is received in a graduated 
test-tube which is kept cool. The distillation is continued until 
the vapors of sulfuric acid begin to appear. The apparatus is 
allowed to cool, the stopper of the retort removed, two cubic cen- 
timeters of water introduced, and the distillation repeated until 
fumes of sulfuric acid are again seen. The distillation with water 
is made twice in order to remove every trace of nitric acid from 
the retort. The distillate is neutralized with a solution of potas- 
sium hydroxid and concentrated to two cubic centimeters, and 
the nitric acid estimated in the manner already described. The 
manganese dioxid used should be previously well washed and 
the sulfuric must be free of nitric acid. 

Preparation of the Indigo Solution. — Fifty grams of indigo in 
fine powder are digested for 24 hours at 40° in a liter of distilled 
water. The water is poured off and replaced with a fresh sup- 



me:thod of^ warington 



429 



ply. After the second decantation the residue is treated with 
750 cubic centimeters of equal parts of water and pure concen- 
trated hydrochloric acid and boiled for an hour. After cooling, 
the undissolved portion is collected on a filter and washed at first 
with hot, and afterwards with cold water, until the filtrate is no 
longer colored and is free of acid. The dried residue is treated 
with ether under a bell- jar, or in a continuous extraction appara- 
tus until the ether is only of a faint blue tint. The 50 grams of 
indigo will yield about 25 grams of the purified article, which, 
however, will still leave a little ash on combustion. 

Solution in Sulfuric Acid. — Five grams of the purified indigo 
are placed in a flask having a ground-glass stopper, treated with 
25 grams of fuming sulfuric acid, and allowed to digest two or 
three days at a temperature of from 50° to 60°. From 70 to 
200 drops of the solution thus made are placed in 100 cubic centi- 
meters of water for use in the process. 

Standardisation of the Indigo Solution. — The solution as pre- 
pared above is standardized by a solution of one gram of pure 
potassium nitrate in 1000 cubic centimeters of distilled water. 
The oxidation of the indigo solution is accomplished as described 
above. Of this strength of standard nitrate solution two cubic 
centimeters are used, corresponding to two milligrams of potas- 
sium nitrate. The indigo solution for this strength potassium 
nitrate solution should have only 20 drops of the sulfuric acid 
solution of indigo to 100 cubic centimeters of water. If 20 grams 
of potassium nitrate are used for 1000 cubic centimeters of the 
standard solution, then 200 drops of the sulfindigotic acid should 
be used to 100 cubic centimeters of water. 

370. Method of Warington. — The modification of the indigo 
method as used by Warington, applicable only in absence of 
organic matter, is the one chiefly employed m England.^^ 

Instead of the ordinary indigo of commerce, indigotin is used. 
The normal solution of the coloring matter is made of such a 
strength as to be equivalent to a solution of potassium nitrate 
containing 0.14 gram of nitrogen per liter. When large quan- 
tities of the coloring matter are to be used, it is advisable to pre- 

^« Journal of the Chemical Society, 1879, 35 : 578. 



K(^ 



I 
I 



if 



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f : 



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430 



AGRICULTURAL ANALYSIS 



pare it about four times the strength given above and then dikite 
it as required. Four grams of subHmed indigotin will furnish 
more than two liters of the color solution. 

The solution is prepared as follows : 

Four grams of indigotin are digested for a few hours with five 
times that weight of Nordhausen sulfuric acid, diluted with water, 
filtered and made up to a volume of two liters. The strength 
<of the indigotin solution is determined with a solution of potas- 
sium nitrate of the strength mentioned above. The process is 
performed as follows : 

From lo to 20 cubic centimeters of the standard nitrate solution 
are placed in a wide-mouthed flask of about 150 cubic centimeters 
capacity. A portion of the indigotin solution is added, such as 
will be deemed sufficient for the process, and the whole is well 
mixed. Strong sulfuric acid is measured from a burette into a 
test-tube, in volume equal to the united volumes of the nitrate solu- 
tion and indigotin. The whole of the sulfuric acid is then poured, 
as quickly as possible, into the solution in the flask and rapidly 
• mixed, and the flask transferred to a calcium chlorid bath, the 
temperature of which should be maintained at 140°. It is essen- 
iial to the success of the operation that the sulfuric acid should 
l)e mixed with the greatest rapidity. It is poured in at once and 
-the whole well shaken without waiting for the test-tube, contain- 
ing the acid, to drain. The flask is covered with a watch-glass 
while it is held in the bath. As soon as the larger part of the - 
-.indigotin is oxidized the flask in the bath is gently rotated. With 
-very weak solutions of nitrate it may be necessary sometimes to 
keep the flask in the bath for five minutes. When the indigo 
color is quickly discharged, it shows the presence of nitric acid 
in considerable excess and a larger quantity of indigo must be 
used in the next experiment. The experiments are continued un- 
til just the quantity of indigotin necessary to consume the nitric 
acid is found, the amount of indigotin being in very slight excess, 
not exceeding one-tenth cubic centimeter of the indigotin solution 
used. The tint produced by the small excess of indigotin re- 
maining is best seen by filling the flask with water. On substances 
^f approximately known strength about four experiments are 



METHOD OF WARINGTON 



431 



usually necessary to determine the proper amount of indigotin, 
but with unknown substances a larger number may be necessary. 
Usually in determinations of this kind it is directed to use 
double the volume of sulfuric acid mentioned above. In this 
case not only is the quantity of indigotin oxidized much greater 
than with a smaller portion of acid, but the prejudicial effect of 
organic matter is also greater when the smaller quantity of acid 

is employed. 

An indigotin solution standardized as above is strictly to be used 
for a solution of nitrate of the strength employed during the stan- 
dardization. The quantity of indigotin oxidized in proportion 
to the nitric acid present diminishes as the nitrate solution 
becomes more dilute. Instead of determining this during each 
series of experiments it may be estimated once for all and a table 
of corrections used. 

The following table is based upon experimental determinations : 



strength 
of niter 
solution 
used. 

/j Normal 



H 
5 

^■r 
4 

3 

2 
Zi 

I 



n 



i i 



i< 



i i 



I i 



t ( 



( ( 



Indigotin 
required, 
cc. 

10.00 
8.71 

7-43 
6.14 

4.86 

3-57 
2.29 

1. 00 



Difference Nitrogen 
between corresponding 
amounts to one cubic 
of indigo- centimeter 
tin, of indigotin, 
gram. 

0.000035000 

0.000035 161 

0.000035330 

0.000035627 

0.000036008 

0.000036763 

0.000038209 

0.000043750 



cc. 
• • • • 

1.29 
1.28 
1.29 
1.28 
1.29 
1.28 



Difference 
between 

the nitrogen 
values, 

gram. 



Difference in the 
nitrogen value 
for a difference 
of one cubic 
centimeter in 
the amount 
of indigotin, 
gram. 



1.29 



O.OOOOOO161 

0.000000169 

0.000000298 

0.000000381 

0.000000756 

0.000001445 

0.000005541 



0.000000125 

0.000000132 

0.000000231 

0.000000298 

0.000000586- 

O.OOOOOII29 

0.000004295 



The table is used as follows : 

Suppose that 20 cubic centimeters of water under examination 
have required 5.36 cubic centimeters of indigotin solution for 
the oxidation of the nitric acid contained therein. By inspec- 
tion of the table it is seen that this number is five-tenths cubic 
centimeter above the nearest quantity given, viz., 4.86 cubic centi- 
meters. From the last column in the table it is found that the 
correction for five-tenths cubic centimeter of indigotin solution 
is 0.000000149 cubic centimeter, being half that for the one cubic 
centimeter given in the table. This is to be subtracted from the 


















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432 



AGRICUIyTURAI, ANALYSIS 



CLASSIFICATION OF METHODS 



433 



unit value in nitrogen given in the first "gram" column of the 
table; viz., 0.000036008. It is thus seen that the 5.86 cubic cen- 
timeters of indigotin solution are equivalent to 0.000035859 gram 
of nitrogen per cubic centimeter. The water under examination, 
therefore, contains nine and six-tenths parts of nitrogen as nitric 
acid per million. 

^ Attention must also be paid in standardizing indigotin solu- 
tions to the initial temperature. A rise in the initial temperature 
will be attended by a diminution in the quantity of indigotin oxi- 
dized. Experiments with a room temperature of 10° and a 
room temperature of 20°, being the initial temperatures of the 
experiments, showed that at the higher temperature the amount 
of indigotin consumed was about five per cent, less when the 
strong solutions of nitrate were employed. The indigotin solution, 
therefore, must be standardized at the same temperature at which 
the determinations are made. 

If 20 cubic centimeters of the standard nitrate solution em- 
ployed be used in setting the indigotin solution, this stand- 
ard will enable the operator to determine nitric acid up to 17.5 
parts of nitrogen per million in water or soil extracts. 

The presence of an abundance of chlorids in the water under 
examination tends to diminish the content of nitric acid found, 
and also tends to introduce an error, which is sometimes of a 
plus and sometimes of a minus quantity, according to the strength 
of the nitric acid present. The reaction is shortened in weak 
solutions by the presence of chlorids, and the quantity of indigotin 
consumed is consequently increased. The error introduced by 
chlorids is usually of an insignificant nature. 

On account of the interference of organic matters with the 
reaction of indigotin it is not of much use in the examination of 
nitrates washed out of soils, although in some cases the results 
may be quite accurate. This method must, therefore, be con- 
sidered as applicable, in general, only to waters or soil extracts 
which contain little or no organic matter. 

In analytical work pertaining particularly to agriculture, the use 
of the indigotin method for determining nitric acid has been 
largely employed, both in the analyses of soil extracts and drain- 



age and irrigation waters. The method, however, can hardly sur- 
vive as an important one in such work in competition with more 
modern, speedy and equally accurate processes of analysis. 

DETERMINATION OF NITRIC NITROGEN BY REDUCTION 

TO AMMONIA 

371. Classification of Methods. — When nitrogen is present 
in a highly oxidized state, e. g., as nitric acid, it may be quickly 
and accurately estimated by reduction to ammonia. This action 
is effected, among other ways, by the reducing power of nascent 
hydrogen, and this substance may be secured in the active state 
by the action of an acid or alkali on a metal, or by means of an 
electric current. The processes depending on the use of a finely 
divided metal in the presence of an acid or alkali have come into 
general use within a few years, and are now employed generally 
instead of the more elaborate estimations depending on the com- 
bustion method by the use of copper oxid or in the colorimetric 
method with indigo. 

The typical reaction which takes place in all cases is repre- 
sented by the following equation : 

2HN03+8H,=2NH3+6H,0. 

The method will be considered under three heads; viz., i. 
Reduction in an alkaline solution ; 2. Reduction in an acid solu- 
tion ; 3. Reduction by means of an electric current. 

In the first class of processes the reduction and distillation 
may go on together. In the second class the reduction is accom- 
plished first and the distillation effected afterwards, with the 
addition of an alkali. In the third class of operations the reduc- 
tion is accomplished by means of an electric current and the 
ammonia subsequently obtained by distillation, or determined by 
nesslerizing. These processes may be applied to the nitrates or 
nitrites as such, or as occurring in rain and drainage waters 
and soil extracts. On account of the ease with which the analyses 
are accomplished, the short time required and the accuracy of the 
results, the reduction methods for nitrates have already com- 
mended themselves to analysts, and are quite likely to supersede all 
others for practical use where small yet weighable quantities of 



!i;; 






434 



AGRICUI.TURAI, ANALYSIS 



halIvE: zinc-iron method 



435 



nitrates are present. For the minute traces of nitrates found in 
rain and drainage waters, and in some soil extracts, the reduction 
method may also be applied, but in these cases the ammonia which 
is formed must be determined colorimetrically (nesslerizing) and 
not by distillation. The processes about to be described are 
especially applicable to the examination of fertilizers containing 
only small quantities of nitrates and of soils and waters rich in 
nitrates. 

REDUCTION IN ALKALINE SOLUTIONS 

372. Extraction of the Nitrates.— Place one kilogram of the dry 
soil or fertilizers poor in nitrates, calculated to water-free sub- 
stance, on a percolator of glass or tin. Moisten the soil thor- 
oughly with pure distilled water, and allow to stand for half an 
hour. Add fresh portions of pure distilled water until the filtrate 
secured amounts to one liter. If the first filtrate be cloudy before 
use it may be refiltered. 

373- Qualitative Test for Nitrates.—Evaporate five cubic centi- 
meters of the extract as obtained above in a porcelain crucible, 
having first dissolved a small quantity of pure brucin sulfate 
therein. When dry, add to the residue a drop of concentrated sul- 
furic acid free of nitrates. If the nitrate calculated as potassium 
nitrate does not exceed the two-thousandth part of a milligram, 
only a pink color will be developed; with the three-thousandth 
part of a milligram, a pmk color with reddish lines; with the 
four-thousandth part of a milligram, a reddish color; with the 
five-thousandth part of a milligram, a distinct red color. 

374- Sodium-Mercury Amalg^am Method.— The reduction is 
effected by means of hydrogen evolved by the action of a prep- 
aration of sodium amalgam. Place 100 cubic centimeters of 
mercury in a flask of half a liter capacity; warm until paraflin 
will remain melted over the surface; drop successively in the 
parafiin-covered mercury pieces of metallic sodium of the size of 
a pea until 6.75 grams have united with the mercury. The amal- 
gam thus prepared contains 0.5 per cent, of metallic sodium and 
may be preserved indefinitely under the covering of paraflin. 

Estimation of the Nitrates.— Jlvaporsitt 100 cubic centimeters 



of the soil extract to dryness on a steam-bath. Dissolve the 
soluble portions of the residue in 100 cubic centimeters of 
ammonia-free distilled water, filtering out any insoluble residue. 
Place the solution in a flask, add 10 cubic centimeters of sodium 
amalgam, stopper the flask with a valve which will permit the 
escape of hydrogen, and allow to stand in a cool room for 24 
hours. Add 50 cubic centimeters of milk of lime and titrate 
the ammonia produced by distillation with standard acid and 
estimate as nitrogen pentoxid. Where the amount of ammonia 
is small, nesslerizing may be substituted for titration. 

375. Method of the Experiment Station at M<>ckern. — The 
principle of this reaction is based on the reducing action exercised 
by nascent hydrogen on a nitrate, the hydrogen being generated 
by the action of soda-lye on a mixture of zinc dust and finely 
divided iron.^^ 

Ten grams of nitrate are dissolved in 500 cubic centimeters of 
water. Of this solution 2^ cubic centimeters, corresponding 
to one-half gram, are placed in a distillation flask of about 400 
cubic centimeters capacity, 120 cubic centimeters of water added, 
and about five grams of well washed and dried zinc dust and an 
e(iual weight of reduced iron. To the solution are added 80 
cubic centimeters of soda-lye of 32° B. The flask is connected 
with the condensing apparatus and the distillation carried on 
synchronously with the reduction, the ammonia being collected 
in 20 cubic centimeters of titrated sulfuric acid. The distillation 
is continued from one to two hours, or until 100 cubic centimeters 
have been distilled, and the remaining sulfuric acid is titrated 
in the usual way. Soil extracts and sewage w^aters should be 
concentrated until they have approximately the proportion of ni- 
trates given above. 

376. The Halle Zinc-Iron Method. — For determining the nitro- 
gen in Chile saltpeter the foregoing method is conducted at 
the Halle Station as follows :^^ Ten grams of the nitrate are dis- 
solved in one liter and 50 cubic centimeters of the solution cor- 

" Bottcher, Die landwirtschaftliclu-n Versiichs-Stationen, 1892. 41 : 165. 
Bieler iind Schneidewiiifl, Die agricultur-chemische Versuchs- 
station, Halle a/S., 1892 : 50. 



;^ i 



9 1 






r 



43^ 



AGRICULTUR.\L ANALYSIS 



INVESTIGATIONS OF B^CK 



437 



responding to half a gram of the sample, used for each deter- 
mination. The apparatus employed is shown in Fig. 7^2. A 
mixture of hve grams of zinc dust and an equal weight of iron 
filings is employed as the source of hydrogen. The reduction 
takes place in an alkaline medium secured by adding to the 
other materials mentioned 80 cubic centimeters of soda-lye of 
1.30 specific gravity. The respective quantities of iron and 
zinc may be measured instead of weighed, as exact proportions 
are not required. After the addition of all the materials the 
flask is allowed to stand for an hour at room temperature. The 
distillation is then commenced and continued until at least 100 
cubic centimeters of distillate have been collected. The receiv- 
ing flasks are ordinary erlenmeyers, each of which contains 20 




Fig. 32. HaUe Nitric Acid Apparatus. 

cubic centimeters of set sulfuric acid, as in the usual kjeldahl 
process. The receiving flasks are sealed with a few drops of 
water by the bulb tubes shown in the figure. After the end of 
the operation the water in each one of the bulb tubes is washed 
back into its proper flask with freshly boiled water. During the 
vigorous evolution of hydrogen at the beginning of the operation, 
some kmd of safety arrangement is necessary to prevent ihe 
particles of soda-lye being carried over by the bubbles of that gas. 
The siphon bulb shown in the figure is found eflfective for this 
purpose. In this operation better results are obtained by condens- 
ing the escaping steam, and for this reason the block tin tubes are 



conducted through a tank supplied with a current of cold water. 
The ends of the tubes should not dip below the surface of the 
liquid in the receivers. When the condensed liquid collects in 
considerable quantities in the safety tube the lamp should be 
extinguished under the flask, which permits the return of the 
liquid to the flask by means of the siphon. This should be done 
two or three times during the progress of the distillation to pre- 
vent a too high concentration of the soda-lye, thus endangering the 
flask. The excess of the acid in the receiver is determined by 
titration, as in the regular kjeldahl method. Blank determina- 
tions are made, from time to time, and corrections made in har- 
mony therewith. 

377. Investigations of Beck. — A late contribution to the 
analysis of Chile saltpeter is that of Beck.^^ 

Beck examined the direct method of Ulsch, subsequently de- 
scribed, and the indirect method which is so commonly em- 
ployed by dealers, depending on the determination of the other 
principal ingredients and subtracting this from 100 to get the per 
cent, of nitrate of soda in the mixture. This last method is par- 
ticularly unsatisfactory, since it gives 1.5 per cent, of sodium ni- 
trate too much. The quantity of perchlorate which is present is 
also important and for technical purposes, such as the nitration 
of cellulose, etc., it is recommended not to use any sample which 
yields more than one per cent, of a sodium salt due to perchlorate. 

Beck expresses the hope that the producers of Chile saltpeter 
in the future will cease to urge the use of the indirect method 
and will refrain from attacking the validity of the direct methods, 
and calls attention to the fact that the increasing possibility of 
producing nitric acid and nitrates directly from the atmosphere 
may supersede the necessity of using the natural salt. 

The factors for calculating the percentage of nitric acid when 
it is reduced to ammonia may be based upon the number of cubic 
centimeters of half-normal sulfuric acid required for 10 cubic 
centimeters of a solution containing 33 grams of sodium nitrate in 
one liter. The factors are as follows : 

^'*' Zeitschrift fiir aiialytische Chemie, 1906, 46 : 669. 



¥ (, 



i 



% 



438 



AGRICUIvTURAL ANAI^YSIS 



< ( 



( ( 



For N : 2.125 (log = 0.32783) 

Nfi, : 8.188 (log '---^ 0.91318) 
NaNOg: 12.893 (log = 1.11318) 

378. Method of Devarda. — The inconvenience due to slow 
action and other causes, arising from the use of pure metals in the 
reduction of nitrates to ammonia, has been overcome, to some 
extent, by Devarda, by use of an alloy, in a state of fine powder, 
consisting of aluminum, copper, and zinc.^^ The alloy consists of 
45 per cent, of aluminum, S'^ P^^ ^^^^t. of copper, and five per 
cent, of zinc. In dissolving, the copper is left in a finely divided 
state, which is a great help in distillation in preventing bumping. 

The analytical process is carried out as follows : The solution 
containing the nitrate, in quantity equivalent to about one-half 
gram of potassium nitrate, is placed in a fiask having a capacity 
of about one liter, and diluted with 60 cubic centimeters of water 
and five cubic centimeters of alcohol, after which 40 cubic cen- 
timeters of caustic potash solution, of specific gravity 1.3 are 
added. From two to two and one-half grams of the alloy de- 
scribed above are introduced, and the flask attached to a conden- 
ser with a receiver containing standard acid. The connection 
between the flask and the condenser is made bv means of a tube 
having on the limb next the flask a bulb filled with glass beads 
to prevent the contents of the flask splashing over into the receiver, 
and on the other limb another bulb to prevent the acid in the re- 
ceiver finding its way into the distillation flask, should Regurgi- 
tation occur. When the flask has been thus connected with the 
condenser it is gently heated for half an hour, at the end of which 
time the evolution of hydrogen will have slackened or ceased, and 
the distillation is then begun, at first cautiously, until the zinc of 
the alloy has completely dissolved, and then more vigorously, the 
time necessary being about 20 minutes from the time when the 
contents of the flask begin to boil. The distillate is caught in 
standard acid and the ammonia determined by titration of the 
residual acid in the ordinary way. It is to be noted that the 
strength of the alkali used is of importance, as, if it be too strong, 
the action on the alloy is unduly vigorous at the beginning of the 

*^ Chemiker-Zeitung, 1892, 16 : 1952. 



VARIATION OF STOKI.ASA 



439 



■■'. i 



operation, and if too weak, the contents of the flask have to be 
heated overmuch, the result in both cases being the formation of 
a fine spray of caustic solution, which is very difilicult to stop, even 
with complicated washing attachments to the distilling flask. The 
test analyses on pure nitrates are satisfactory. This method has 
been used with satisfaction in the laboratory of the Bureau of 
Chemistry, but does not appear to have any special advantage 
over the process of Ulsch, to be described further on. 

379. Variation of Stoklasa. — Stoklasa has subjected the 
method of Devarda to a comparative test with the following 
methods :^^ 




^ig- 33- Stoklasa's Nitric Acid Apparatus. 

1. Wagner's schloesing-grandeau method. 

2. Lunge's nitrometer method. 

3. Stutzer's method. 

. The reduction takes place in a copper erlenmeyer A, Fig. }^2^, in 
which, in addition to the solution containing the nitrate, are placed 
200 cubic centimeters of water, 40 cubic centimeters of potassium 
hydroxid solution of 33° B., ^\e cubic centimeters of alcohol, and 
finally two and one-half grams of the finely powdered devarda 
alloy. The distillate passes through a tube B filled with glass 
pearls and into the condenser D through the bulbs CC. 
^* Zeitschrift fiir angewaudte Chemie, 1893, 6 : 161. 



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440 



AGRICULTURAL, ANALYSIS 



After the flask is connected with the distilling apparatus, it is 
gently warmed and the reduction is ended in about 20 minutes. 
The ammonia which is formed is distilled into E, containing the 
standard acid S, requiring about 20 minutes more. The com- 
parative results given, show that the devarda method is equally 
accurate as any of the other methods mentioned, giving prac- 
tically theoretical results. 

In so far, however, as speed of an analysis is concerned, the 
first place is awarded to the lunge nitrometer method, with which 
a complete analysis can be made in from 30 to 40 minutes. In 
the second rank, so far as speed is concerned, the devarda method 
is recommended. All the methods give accurate results. 

380. Method of Sievert. — Two grams of potassium or sodium 
nitrate are dissolved, and the solution made up to 1000 cubic cen- 
timeters.^- Fifty cubic centimeters of the solution are placed in 
a 600 cubic centimeter flask and diluted with 50 cubic centimeters 
of water, and from 18 to 20 grams of caustic alkali added. After 
the alkali is dissolved, 75 cubic centimeters of 96 per cent, alcohol 
are added and a few pieces of bone-black to prevent foaming. 
From 10 to 15 grams of zinc or iron dust are added to the flask 
which is closed and connected with a U-tube holding about 200 
cubic centimeters, which contains about 10 cubic centimeters of 
normal sulfuric acid. This U-tube is kept cool by being immersed 
in water. The whole mixture is allowed to stand for three 
or four hours and the alcohol is distilled slowly, the ammo- 
nia formed by the reduction of the nitrates being carried over with 
it. The distillation lasts for about two hours. The- contents 
of the U-tube are carefully rinsed into a dish and the excess of 
sulfuric acid titrated with one-fourth normal soda-lye. 

For soil extracts and substances containing unknown quan- 
tities of nitric acid, a preliminary test will indicate approxi- 
mately the amount thereof, and this will be an indication for 
the quantity to be used in the analysis. 

The method of Stutzer diflfers from the foregoing in the em- 
ployment of aluminum dust instead of iron or zinc.^^ The reducing 

" Liebig's Annalen der Chemie, 1862, 125 : 293. 
^ Zeitschrift fur angewaiidte Chemie, 1890, 3 : 695. 



IS 



1 V 



VARIATION O^ the: SODIUM-AMALGAM PROCESS 



441 



power of aluminum, however, varies greatly according to the 
method in which the metal has been prepared. Pure aluminum 
prepared by the electric method, reduces the nitric acid much 
less vigorously than the metal prepared by the older methods of 
fusion with sodium. For this reason the method of Stutzer is 
not to be preferred to that of Sievert. 

REDUCTION IN AN ACID SOLUTION 

381. Variation of the Sodium- Amalgam Process. — This method 
is described by Monnier and Auriol.^* 

The principle of the operation depends on the reduction of 




Fig. 34, Apparatus of Monnier and Aviriol. 

the dissolved nitrate by titrated sodium amalgam in presence of 
an acid, and the estimation of the quantity of nitric acid present 
from the deficit in the volume of hydrogen. The apparatus em- 
ployed is conveniently mounted as shown in Fig. 34. The brass 
vessel A is movable by means of the cord on the pulley B, in such 

*'* Archives des Sciences physiques et ualurelles, Geneve, 1894, [3], 
31 :352. 






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442 



AGRICUI.TURAL ANALYSIS 



a way as to be fixed at any required altitude. It is filled with 
water and connected by a rubber tube to the cooling tube D. 
Within the cooling tube there is a graduated cylinder open at its 
lower end. Its upper end is connected directly with the apparatus 
C. The cooling tube D has a small side tube c near its upper 
end, by means of which the air can enter or escape when the 
position of A is changed. The apparatus C, in which the reaction 
takes place, is a glass cylinder. Its upper end is continuous with 
the T-tube pravided with the stop-cocks a and h. One arm of 
the T permits connection with the graduated measuring tube by 
means of a rubber union. The lower end of C is clos-d with a 
large hollow ground-glass stopper, carrying a small receptacle 
within, so that it forms two separate water-tight compartments, 
open at the top. 

The sodium amalgam is prepared as follows : 

In a clay crucible are heated 400 grams of mercury, and, 
little by little, with constant stirring, four grams of dry sodium 
are added. When cold, the amalgam is placed in a burette, hav- 
ing a ground-glass stopper, and covered with petroleum. The 
strength of the amalgam is established in the following manner. 
A small glass thimble, ground even at the top, is filled with the 
amalgam and struck off even with a ground-glass straight edge. 
In this way the same quantity of amalgam is taken for each test. 
This measured portion of the amalgam is placed in the inner ves- 
sel of the glass stopper to C. Ten cubic centimeters of water, con- 
taining 60 centigrams of tartaric acid, are placed on the outer ring 
of the glass stopper, which is then inserted, well oiled, in C, clos"^ 
ing it air- and water-tight. The tartaric acid solution 'also carries 
a piece of litmus paper, so that its constant aciditv may be in- 
sured. The vessel A is fixed in a position which brings the water 
ni the graduated burette and tube D exactly to the o mark. The 
cock a is closed, b opened, and C is inverted until all the amalgam 
IS poured into the solution of tartaric acid. The evolved hydro- 
gen mixed with the air contained in the apparatus, is passed into 
the graduated burette. After 15 minutes, the reaction is ended. 
The water level within and without the graduated tube is restored 



ME:TH0D 01^ SCHMITT 



443 



and the volume of gas evolved noted and reduced by the usual 
tables to 0° and 760 millimeters pressure of the barometer. 

An amalgam prepared as above gives about three cubic centi- 
meters of hydrogen for each gram. The thimble holds from 12 
to 15 grams. 

The estimation of nitric acid is made in a solution containing 
about one-tenth per cent, of nitrate. Ten cubic centimeters are 
used, to which six-tenths gram of tartaric acid is added, and placed 
in the outer part of the glass stopper. The rest of the process is 
conducted exactly as described above. The deficit in hydrogen 
is calculated to nitrogen pentoxid. 

The reduction by sodium amalgam is not so convenient a form 
of estimating nitric acid as many of the other forms of using 
r.ascent hydrogen. As practiced by calculating from the deficit 
of hydrogen, however, it has some advantages by reason of the 
fact that no heating is required. The presence of organic neu- 
tral bodies, or even those of an acid nature, like humus, does not, 
therefore, interfere with the work. Likewise, mineral bodies 
in solution, which are not reduced by nascent hydrogen, do not 
interfere with the accuracy of the reaction. 

382. Method of Schmitt. — In the method of Schmitt 40 cubic 
centimeters of glacial acetic acid are placed in a flask of 600 cubic 
centimeters content, and 15 grams of a mixture of zinc and iron 
dust added.^^ To this quantity of the solution containing the 
nitrate, representing about half a gram of the pure nitrate, is added 
with constant shaking, in portions which do not evolve hydrogen 
too rapidly. After about 15 minutes when the evolution of hydro- 
gen has somewhat diminished, an additional 15 grams of the 
metal dust are added. If the contents of the flask become thick 
they are diluted with water. The reduction is complete in from 
30 to 40 minutes. The contents of the flask are saturated with 
enough soda-lye not only to neutralize the excess of acetic acid, 
but to keep the zinc hydroxid also in solution. For this purpose 
about 200 cubic centimeters of soda-lye of T.25 specific gravity are 
necessary. The ammonia is obtained by distillation into standard 
acid in the usual way. 

05 Cheniiktr-ZL*ituiig, 1890, 14 : 1410. 



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444 



AGRICULTURAI, ANALYSIS 



ULSCH METHOD 



445 



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The flask is covered during the reduction to prevent loss by 
spraying. It must be noted that it is essential that the iron be 
finely divided ; it is mixed with the powdered zinc in equal parts. 

The total nitrogen can be determined in guanos and nitrate 
mixtures by the following simple alteration in procedure: One 
gram of the substance is dissolved in water, five cubic centimeters 
of glacial acetic acid, an<l from two to three grams of the mixed 
metallic powder added, and the whole gently heated for lo or 15 
minutes. After the contents of the flask have cooled, 25 cubic 
centimeters of sulfuric acid are cautiously added in small portions, 
undue frothing being restrained by the addition of a fragment 
of paraffin wax. The acetic acid is driven off bv heating, and the 
remaining contents of the flask boiled until the organic matter is 
completely decomposed as in the kjeldahl process. About two 
hours boiling is required. Neutralization and distillation are ac- 
complished as in the ordinary manner. The method is also ap- 
plicable to the determination of nitrates in drinking water, provid- 
ed nitrites and ammonia be absent. 

383. Method of Ulsch.— In practice the method of Ulsch has 
come into general use."" 

For the determination of nitrogen in nitrates by this method 
halt a gram of saltpeter or four-tenths gram of sodium nitrate 
is dissolved in 25 cubic centimeters of water, in a flask with a 
content of about fxxy cubic centimeters. Five grams of iron re- 
duced by hydrogen, and 10 cubic centimeters of sulfuric acid 
diluted with two volumes of water are then added to the flask 
To avoid mechanical losses during the evolution of hydrogen a 
pear-shaped glass stopper is hung in the neck of the flask After 
the first violent evolution of hydrogen has passed, the flask is 
slowly heated until, in about four minutes, it is brought to a gentle 
bo,l. The boihng is continued for about six minutes when the 
reduction is complete. About 50 cubic centimeters of water are 
added, an excess of soda-lye and a few particles of zinc ; then the 
ammonia is distilled and collected i„ standard acid in the usual 
way. 

The method of Ulsch can also be applied, according to Fricke, 

«« Chemisches Central-BIatt, 1890, 2 : 926. 



to the analysis of nitrates contained in drinking and drainage 
waters, and it is regarded by him as one of the best methods to 
be employed in such investigations/'^ 

The method of Ulsch has given entirely satisfactory results, and 
is generally used in preference to other methods in cases where 
a considerable quantity of nitrates is present. It is based on the 
following reactions : 

2KN03+H3SO,=:K,SO,+2HN03 
2HN03+8H,=2NH3+6H.O 
2NH3+H,s6,= ( NH,) ,s6,. 

384. Ulsch Method Applicable to Mixed Fertilizers. — The 
method of Ulsch, which is found to give good results with pure 
nitrates or with nitrates in the absence of other forms of nitrogen, 
may also be adapted to mixed fertilizers containing nitrogen in 
more than one form. Street has developed such a method and 
shown, by analytical data, that it is applicable in a great num- 
ber of cases.^** The variation is based on the substitution of mag- 
nesia for soda in the distillation and is carried on as follows : 

Place one gram of the sample in a half-liter flat-bottomed flask. 
Add about 30 cubic centimeters of water, one gram of reduced 
iron, and 10 cubic centimeters of sulfuric acid diluted with an 
equal volume of water, shake well, and allow to stand for a 
short time. This will remove the danger of an explosion caused 
by the otherwise violent action whicii takes place. Close the 
neck of the flask with a rubber stopper through which passes a 
glass dropping-bulb filled with water. The flask having been 
stoppered, place it on a slab to which a moderate heat is applied. 
Allow the solution to come slowly to a boil and then boil for 
five minutes and cool. Add about 100 cubic centimeters of water, 
a little paraflin, and about five grams of magnesium oxid. Boil 
for 40 minutes, after which time all the ammonia will be dis- 
tilled, and collect the ammonia in set acid. 

The magnesia causes a slight frothing, which can easily be 
controlled by adding a little paraffin and by bringing to a boil 
very gradually. Fully 40 minutes are necessary to distil all the 

*'' Zeitschrift fiir angewandte Clieinie, 1891, 4 : 241. 
^ Division of Chemistry, Bulletin 35, 1892 : 88. 



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446 



AGRICULTURAL ANALYSIS 



ammonia. Tests were made after boiling for 30 minutes and 
traces of an]monia were still found ; after 40 minutes these traces 
entirely disappeared. 

The method is a quick one. One man can easily do six deter- 
minations at a time, and these six determinations can be made 
in but a little over an hour. Magnesia gives results closely agree- 
ing with theory and causes a very slight frothing, which can be 
easily controlled. One gram of reduced iron is sufficient in all 
ordinary complete fertilizers. 

Magnesia is preferred to caustic soda in the distillation be- 
cause it produces less frothing and by reason of the danger of 
some of the soda-lye being carried over mechanically and thus 
tending to produce an error of a plus nature. In the use of mag- 
nesia, assurance must be had that it is strongly in excess. Being 
less active in its effects, a longer time for the distillation must 
be taken than when soda-lye is used. The modified ulsch method 
just described is recommended provisionally, and with the expec- 
tation that each analyst will ascertain its true merits before allow- 
ing it to displace longer approved processes. 

385. Kruger's Method for Nitric Acid. — About 0.3 gram of 
the nitrate dissolved in water is mixed with 20 cubic centimeters 
of a hydrochloric acid solution of stannous chlorid holding 150 
grams of tin per liter.^^ One and a half grams of spongy tin 
prepared by the action of zinc on stannous chlorid are added. 
The flask containing the mixture is heated until the tin is dis- 
solved, by which time the nitric acid is completely reduced. The 
subsequent distillation and titration are accomplished as usual. 
In the case of nitro and nitroso compounds, after the solution of 
the tin, 20 cubic centimeters of sulfuric acid are added and 
heated